- #1
karseme
- 15
- 0
So, I've got an assignment to prove that [tex] f(x)=\cos{(n \cdot \arccos{x})} [/tex] is a polynomial for [tex] \forall n \in \mathbb{N} [/tex]. Also, we were suggested to use mathematical induction. So, I've tried:
Base step: [tex] n=1 \implies f(x)=\cos{(\arccos{x})}=x[/tex]
Assumption step: [tex] f(x)=\cos{(n \cdot \arccos{x})}, \forall n \in \mathbb{N} [/tex]
Induction step: [tex] f(x)=\cos{((n+1) \cdot \arccos{x})}=\cos{(n \arccos{x}+\arccos{x})}=\cos{(n \arccos{x})}\cos{( \arccos{x})}-\sin{(n \arccos{x})}\sin{( \arccos{x})}=f(x) \cdot x -\sin{(n \arccos{x})}\sin{( \arccos{x})}[/tex]
And I don't know what to do with sine.
Base step: [tex] n=1 \implies f(x)=\cos{(\arccos{x})}=x[/tex]
Assumption step: [tex] f(x)=\cos{(n \cdot \arccos{x})}, \forall n \in \mathbb{N} [/tex]
Induction step: [tex] f(x)=\cos{((n+1) \cdot \arccos{x})}=\cos{(n \arccos{x}+\arccos{x})}=\cos{(n \arccos{x})}\cos{( \arccos{x})}-\sin{(n \arccos{x})}\sin{( \arccos{x})}=f(x) \cdot x -\sin{(n \arccos{x})}\sin{( \arccos{x})}[/tex]
And I don't know what to do with sine.