
This paper gives a detailed study of a new generation of dual Jacobsthal and dual Jacobsthal-Lucas numbers using dual numbers. Also some formulas, facts and properties about these numbers are presented. In addition, a new dual vector called the dual Jacobsthal vector is presented. Some properties of this vector apply to various properties of geometry which are not generally known in the geometry of dual space. Finally, this study introduces the dual Jacobsthal and the dual Jacobsthal-Lucas numbers with coefficients of dual numbers. Some fundamental identities are demonstrated, such as the generating function, the Binet formulas, the Cassini's, Catalan's and d'Ocagne identities for these numbers.
Citation: Faik Babadağ. A new approach to Jacobsthal, Jacobsthal-Lucas numbers and dual vectors[J]. AIMS Mathematics, 2023, 8(8): 18596-18606. doi: 10.3934/math.2023946
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This paper gives a detailed study of a new generation of dual Jacobsthal and dual Jacobsthal-Lucas numbers using dual numbers. Also some formulas, facts and properties about these numbers are presented. In addition, a new dual vector called the dual Jacobsthal vector is presented. Some properties of this vector apply to various properties of geometry which are not generally known in the geometry of dual space. Finally, this study introduces the dual Jacobsthal and the dual Jacobsthal-Lucas numbers with coefficients of dual numbers. Some fundamental identities are demonstrated, such as the generating function, the Binet formulas, the Cassini's, Catalan's and d'Ocagne identities for these numbers.
In 1873, W. K. Clifford initiated the study of dual numbers and these numbers were used at the beginning of the twentieth century by the German mathematician Eduard Study, who studied line geometry and kinematics to obtain the dual angle which measures the relative position of two skew lines in space. This study defines a dual angle as θ+dε, where θ is the angle between the directions of two lines in three-dimensional space and d is a distance between them, [1,2,3].
In this paper, our objective is to conduct a detailed study of a new generation of the dual Jacobsthal number and dual Jacobsthal-Lucas numbers. We describe a new dual Jacobsthal vector to apply in the geometry of dual space.
A dual number is described as U=u+εu∗, where u and u∗ are real numbers and ε is a symbol taken to satisfy ε2=0 with ε≠0.
The addition and multiplication of two dual numbers U=u+εu∗ and V=v+εv∗ are defined by
U+V=(u+v)+ ε(u∗+v∗) |
and
UV=uv+ε(uv∗+u∗v), |
respectively. In mathematics and physics, vector is a term that refers to some quantities that cannot be expressed by a single number (a scalar) or to elements of some vector spaces as in [4].
The dual vector D3 is defined by
→U=→u+ε→u∗ ;→u,→u∗ϵR3=(u1+εu∗1,u2+εu∗2,u3+εu∗3). |
The scalar product and cross product of dual vectors →U=→u+ε→u∗ and →V=→v+ ε→v∗ are
⟨→U,→V⟩=⟨→u,→v⟩+ε(⟨→u,→v∗⟩+⟨→u∗,→v⟩), | (1.1) |
and
→U×→V=⟨→u,→v⟩+ε(→u×→v∗+→u∗×→v), | (1.2) |
respectively.
The norm of the dual vector →U is given by
‖→U‖=‖→u‖+⟨→u,→u∗⟩‖→u‖. |
Proposition 1. →U is dual unit vector if and only if ‖→u‖=1 and ⟨→u,→u∗⟩=0 [1].
The Jacobsthal numbers and the Jacobsthal-Lucas numbers are given by the second-order recurrence relations as follows:
Jn=Jn−1+2Jn−2,J0=0,J1=1, |
and
jn=jn−1+2jn−2,j0=2, j1=1, |
respectively, [5,6,7,8,9,10,11,12]. Also these numbers each have another expression of the respective forms
Jn=αn−βn α−β=2n−(−1)n3, | (1.3) |
and
jn=αn+βn=2n+(−1)n. | (1.4) |
The dual Jacobsthal numbers and the dual Jacobsthal-Lucas numbers, respectively, are as follows:
Jn=Jn+εJn+1, | (1.5) |
and
jn=jn+εjn+1, | (1.6) |
where ε2=0 with ε≠0.
In this section, we obtain some fundamental identities such as the generating function, the Binet formulas, the Cassini's, Catalan's and d'Ocagne identities for the dual Jacobsthal numbers and the dual Jacobsthal-Lucas numbers.
Theorem 1. The generating function of Jn is
h(t)=J0(1−t)+ J1t1−t−2t2. |
Proof. If h(t) is a generating function for Jn, then
h(t)=∞∑i=0Jiti. |
Multiply the function h(t) by t and t2, respectively. We can write
th(t)=J0t+J21t+...+Jn+1nt,t2h(t)=J0t2+J1t3+...+Jntn+2. |
Doing the needed arrangements, we will have
h(t)(1−t−2t2)=J0+t(J1−J0),h(t)=∞∑i=0Ji ti |
which is the desired result.
Theorem 2. Let Jn and Jm be dual Jacobsthal numbers. For every m,n≥1,
JnJm+Jn+1Jm+1=19(jn+m−2m(−1)mjn−m)+ε19(2n+m+4+12Jn+m+2m(−1)mjn−m). |
Proof. By using the equalities (1.3)–(1.5), and doing the necessary calculations, we will have
JnJm+Jn+1Jm+1=Jn Jm+Jn+1Jm+1+ε(Jn+1Jm+JnJm+1+Jn+1 Jm+2+Jn+2Jm+1)=19(αn+m+βn+m)−19(αnβm+αnβm)α−mβ−mα−mβ−m+ε(16αn+m9+4(αn+m−βn+m)3+19(αnβm+αnβm)α−mβ−mα−mβ−m)=19(αn+m+βn+m)−19(αnβm+αn βm)α−mβ−m α−mβ−m+ε19(2n+m+4+12Jn+m+2m(−1)mjn−m)=19(jn+m−αmβmjn−m)+ε19(2n+m+4+12Jn+m+2m(−1)mjn−m). |
Theorem 3. (Binet formulas) For every positive integer n, the following equalities hold
Jn=α_αn−β_βn3, | (2.1) |
and
jn=α_αn+β_βn | (2.2) |
where
α_=1+εα and β_=1+εβ. | (2.3) |
Proof. By using the Binet formula for dual Jacobsthal number Jn, we obtain
Jn=α_αn−β_βn3=(1+εα)2n−(1+εβ)(−1)n3=2n−(−1)n+ε(2n+1−(−1)n+1)3=Jn+Jεn+1. |
If calculations are made similarly for the dual Jacobsthal-Lucas numbers, we obtain
jn=α_αn+β_βn=(1+εα)2n+(1+εβ)(−1)n=jn+εjn+1. |
Theorem 4. (Catalan identity) For the integers n,r such that n≥r, then Catalan's identity is as follows:
Jn+rJn−r−J2n=(−1)n2n9((−1)r+12r J2r+ ε(2−jr+1)). |
Proof. Using the relation in the equality (1.5), we can write
Jn+rJn−r−J2n=Jn+rJn+r−J2n+ε( Jn+rJn−r+1+Jn+r+1 Jn−r−2Jn Jn+1). |
From the equalities (1.3) and (1.4), we will have
Jn+rJn+r−J2n=− αn+rβn+(αr− βr3)2=19(−1)n+r+12n+r J2r, |
and
ε(Jn+rJn−r+1+Jn+r+1 Jn−r−2Jn Jn+1)=19αnβn(2−αr+1− βr+1)=19(−1)n2n(2−jr+1); |
we obtain that
Jn+rJn−r−J2n=(−1)n2n9((−1)r+12r J2r+ ε(2−jr+1)). |
Theorem 5. (Cassini identity) For n≥1, we have
Jn+rJn−r−J2n=(−1)n2n9(2−3ε). |
Proof. If we write r=1 in Theorem 4, the proof is completed.
Theorem 6. (d'Ocagne's identity) For any integer n and m, we have
Jm+1Jn−JmJn+1=(−1)m2mJn−m(1+ε). |
Proof. From the equality (1.5)
Jm+1Jn−JmJn+1=JnJm+1−Jn+1Jm+ε(JnJm+2−Jn+2Jm). | (2.4) |
From the equalities (1.3) and (1.4), and a straightforward computation, we have
JnJm+1−Jn+1Jm=(αn−βn3 αm+1−βm+13−αn+1−βn+13αm−βm3)α−mβ−m−m β−m=19αmβm(αn−m−βn−m)=αmβmJn−m |
where from the last equality, we will have
JnJm+1−Jn+1 Jm=2m(−1)m Jn−m | (2.5) |
and
ε(JnJm+2−Jn+2Jm)=ε2m(−1)m Jn−m. | (2.6) |
Substituting the equalities (2.5) and (2.6) in (2.4), we obtain
Jm+1Jn−JmJn+1=(−1)m2mJn−m(1+ε). |
In this part, we will give dual Jacobsthal vectors and geometric properties of them.
A dual Jacobsthal vector in D3 is given by
→Jn=→Jn+ε→Jn+1, |
where
→Jn=(Jn,Jn+1,Jn+2) and →Jn+1=(Jn+1,Jn+2,Jn+3) | (3.1) |
are real vectors in R3.
Theorem 7. If →Jn is a dual unit vector, then
7(−1)n4n+(−1)n2n−2=0 or jn=7(−1)n22n+1. |
Proof. By using the equalities (1.1), (1.3), (1.5) and (3.1), we get the following statements:
‖→Jn‖=√J2n+J2n+1+J2n+2=√(αn−βn3)2+(αn+1−βn+13)2+(αn+2−βn+23)2=√21α2n+3β2n+6 αnβn9=√7.4n+2n(−1)n+13 |
and
⟨→Jn,→Jn+1⟩=JnJn+1+Jn+1Jn+2+Jn+2Jn+3. | (3.2) |
Doing the necessary calculations, we will have
⟨→Jn,→Jn+1⟩=7.22n+1−(−1)njn3. |
Using proposition 1 and above calculations, we easily reach the result.
Theorem 8. Let →Jn and →Jm be dual Jacobsthal vectors. The scalar and cross products of →Jn and →Jm are
⟨→Jn,→Jm⟩=73jn+m(1+4ε)+2m(−1)m3jn−m(1+ε), | (3.3) |
and
→Jn×→Jm=2n(−1)njn−m(1+ε)(2→e1+→e2−→e3). |
Proof. From the equalities (1.1), (1.4), (1.6) and (3.2),
⟨→Jn,→Jm⟩= JnJm+Jn+1Jm+1+Jn+2Jm+2+ε(JnJm+1+JmJn+1+Jn+1Jm+2+Jn+2Jm+1+Jm+3Jn+2+Jn+3Jm+2). |
By doing the necessary calculations, we obtain
=JnJm+Jn+1Jm+1+Jn+2Jm+2=73(αn+m+βn+m)+αmβm9(1+αβ+α2β2)(αn−m+βn−m)=73jn+m+2m(−1)m3jn−m |
and
JnJm+1+JmJn+1+Jn+1Jm+2+Jn+2Jm+1+Jm+3Jn+2+Jn+3Jm+2=283(αn+m+βn+m)−19(α+β)(1+αβ+ α2β2)(αnβm+αmβn)=283(αn+m+βn+m)−19(α+β)(1+αβ+ α2β2)(αnβm+αmβn)α−mβ−mα−mβ−m. |
In the last equality, we take into account that α=2 and β=−1; thus, we obtain
=283jn+m−2m(−1)m3jn−m. |
From the equalities (1.2), (1.3), (1.5) and (1.6), we obtain
→Jn×→Jm=→Jn×→Jm+ε(→Jn×→Jm+1+→Jn+1×→Jm). | (3.4) |
We compute the following expressions:
→Jn×→Jm=[→e1→e2→e3JnJn+1Jn+2JmJm+1Jm+2]=(−1)m2mJn−m(−2→e1−→e2+→e3). | (3.5) |
In the equality (3.4), if the dual part is calculated similarly, then
→Jn×→Jm+1+→Jn+1×→Jm=(−1)m2mJn−m(−2→e1−→e2+→e3). | (3.6) |
Substituting the equalities (3.5) and (3.6) in (3.4), we obtain
→Jn×→Jm=(−1)m2mJn−m(−2→e1−→e2+→e3)(1+ε). |
Proposition 2. (E. Study mapping) Let →U= →u+ε→u∗ be the unit dual vector corresponding to the directed line l in R3. The unit real vector →u is the direction vector of the line l, and the real vector →u∗ determines the position of l [2] (see Figure 1).
Proof. Let us consider a dual unit vector →U=→u+ε→u∗. The directed line corresponding with →U is in the direction of →u according to the E. Study mapping; let P,X be points on the line and the origin be considered as the point O. Then, the line equation is given by
→OX=→OP+r→u, |
where r∈I⊂R is a parameter. A point P is on the line of vectors →u,→u∗ if and only if
→u×→u∗= →u×(OP×→u), |
and then
→OP=→u×→u∗+⟨→u,→OP⟩→u, |
and
→OX=→u×→u∗+(⟨→u,→OP⟩+r)→u. |
By taking a new parameter t=⟨→u,→OP⟩ +r and →OX=→x, we will have the result as
→x=→u×→u∗+t→u. | (3.7) |
Theorem 9. If →J0n is a dual Jacobsthal vector and its unitized vector of →J0n is →Jn=→Jn+ ε→Jn+1, whose terminal point is on the dual unit sphere, then the equation of the oriented line that corresponds to →Jn in R3 is given by
→xn=(−1)n2n(29+tJn)→e1+(tJn+1)→e2+819+tJn+2)→e3), |
where t∈I⊂R is a parameter.
Proof. By using the equalities (1.2), (1.3), (1.5) and (3.6), we obtain the equation of the oriented line which corresponds with →Jn as follows:
→xn=→Jn×→Jn+1+t→Jn,=[→e1→e2→e3JnJn+1Jn+2JmJm+1Jm+2]+t(Jn→e1+Jn+1→e2+Jn+2→e3)=(−1)n2n(29+tJn)→e1+(tJn+1)→e2+(19+tJn+2)→e3). |
Definition 1. (Dual angle)The dual angle represents the relative displacement and orientation between two lines d1 and d2 in D3. The dual angle is defined as
φ=θ+εθ∗. |
This concept was given by Study in 1903. θ the primary component of θ∗ is the projected angle between d1 and d2, and θ∗ is the shortest distance between lines d1 and d2 (see Figure 2).
The scalar product of any unit dual vectors →U=→ u+ε→u∗ and →V=→v+ ε→v∗ is obtained as follows:
⟨→U,→V⟩=cos φ=cosθ− εθ∗sinθ, | (3.8) |
where φ=θ+εθ∗ is a dual angle [2].
Theorem 10. From equalities (3.3) and (3.8), the scalar product of →Jn and →Jm is
⟨→Jn,→Jm⟩=7jn+m+2m(−1)mjn−m3+ε28jn+m+2m(−1)mjn−m3,=cosφ=cosθ− εθ∗sinθ. |
In the last the equality, φ is a dual angle if and only if the following cases are true.
Case 1. If cosθ = 0 and θ∗≠ 0, then
⟨→Jn,→Jm⟩=cosφ=− εθ∗, |
where
−28jn+m+2m(−1)mjn−m3=θ∗. |
Therefore, lines →Jn and →Jm are perpendicular but not intersecting.
Case 2. If θ∗ = 0, then
⟨→Jn,→Jm⟩=cosφ=cosθ=7jn+m+2m(−1)mjn−m3θ=cos−1(7jn+m+2m(−1)mjn−m3), |
lines →Jn and →Jm are intersecting.
Case 3. If θ = π2 and θ∗ = 0, then
⟨→Jn,→Jm⟩=cosφ=cosπ2=7jn+m+2m(−1)mjn−m3, |
the last equality is
jn+mjn−m=2m(−1)m+17, |
and lines →Jn and →Jm are perpendicular and intersecting.
Case 4. If θ = 0, then
cosφ=1,ε=3−722n+1−(−1)njn28j2n+1−2n(−1)n. |
Thus, lines →Jn and →Jm are parallel.
In this study, the dual Jacobsthal numbers and the dual Jacobsthal-Lucas numbers with coefficients of dual numbers have been introduced. We obtained some fundamental identities such as the generating function, the Binet formulas, the Cassini's, Catalan's and d'Ocagne identities for these numbers. In addition, some properties of dual Jacobsthal vectors to exert in geometry of dual space are obtain.
The authors declare they have not used Artificial Intelligence (AI) tools in the creation of this article.
The author would like to express their sincere thanks to the editor and the anonymous reviewers for their helpful comments and suggestions.
There are no competing interests.
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