could you help me with one more thing? @satellite73

Question

anonymous · Answer

sure if i know it

solomonzelman · Answer

you know it.

anonymous · Answer

how can  I derivate double Angle Formulas from the sum of Two Angles?

anonymous · Answer

by changing $2x$ in to $x+x$ and using it 
i.e put 
$$\sin(x+y)=\sin(x)\cos(y)+\cos(x)\sin(y)$$  and make it 
$$\sin(x+x)=...$$

anonymous · Answer

in simple english, where you see a $y$ replace it by an $x$

anonymous · Answer

oh ok so I'm allowed to just do that?

anonymous · Answer

i give you permission,
don't tell

anonymous · Answer

lol yes
 you get it essentially in one step

anonymous · Answer

haha alright thanks again :)

anonymous · Answer

yw
since you probably have the double angle formula written down you can check that your answer is correct
you will get 3 different ones for the double angle formula for cosine
that one turns out to be most useful