I think of eiθ=cosθ+isinθ......
Let me try :) (Im just a kid don't blame me if I did anything wrong....... Just point out the mistake......)
4sinx=ex4sinx=e(i4⋅x)i4=14sinx=ei⋅(xi3)4sinx=ei⋅(−ix)i3=−i4sinx=cos(−ix)+isin(−ix)
We are going to introduce 4 formulae here:
1) sin(−x)=−sinx
2)cos(−x)=cosx
3)cos(ix)=coshx=ex+e−x2
4)sin(ix)=isinhx=e−x−ex2i
Now continue.....
Last step done was:
4sinx=cos(−ix)+isin(−ix)4sinx=cos(ix)−isin(ix)Formulae 1 and 24sinx=ex+e−x2+ex−e−x2=exFormulae 3 and 4
Nope it just goes back to 4 sin x = e^x....... Sob sob :(
Another method!!
4sinx=ex
We are going to introduce the definition of sin x this time....... (If it doesn't work Im going to use Taylor series :( )
4(eix−e−ix2i)=ex2eix−2e−ixi=ex2ie−ix−2ieix=ex1i=−i2i(1eix−eix)=ex2i(1−e2ixeix)=ex
Np.
I never give up!!!
Another method!!
4(x−x33!−x55!+x77!+x99!⋅⋅⋅)=ex
Still np......
Sigh maybe I am just too dull and can't see the method......
PS I am 14 :)