Find the sum of following series:
1+cosθ+12!cos2θ+⋯
where θ∈R.
My attempt: I need hint to start.
Answer
Hint:
1+cosx+12!cos2x+…=ℜ(e0ix+e1ix+12!e2ix+…)=ℜeeix
eix=cosx+isinx⟹eeix=ecosxeisinx=ecosx(cos(sinx)+isin(sinx))
Your sum is
ecosxcos(sinx)
Find the sum of following series:
1+cosθ+12!cos2θ+⋯
where θ∈R.
My attempt: I need hint to start.
Answer
Hint:
1+cosx+12!cos2x+…=ℜ(e0ix+e1ix+12!e2ix+…)=ℜeeix
eix=cosx+isinx⟹eeix=ecosxeisinx=ecosx(cos(sinx)+isin(sinx))
Your sum is
ecosxcos(sinx)
How to find lim without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...
No comments:
Post a Comment