Question

cos(a+b+c)

Answer 1

\[\cos(a+b+c)+isin(a+b+c)=e^{i(a+b+c)}=e^{ia}*e^{ib}*e^{ic}=[\cos(a)+isin(a)]*[\cos(b)+isin(b)]*[\cos(c)+isin(c)]\]

Take the real part of that.

Answer 2

Or ask a question and maybe I can help more. ;P

Answer 3

Tnks But Your ansewr is so difficlt for me i mean this is not what im styding now

Answer 4

No problem! =D What's your question?

Answer 5

Find what that mean ? cos(a+b+c)= ?

Answer 6

Well suppose you know what cos(90) is, then you know what cos(30+60) is right?

Answer 7

No i want the ansewr for my question like this sin(A + B + C) = sin(A + B) cosC + sinC cos(A + B)
= [sinAcosB + sinBcosA]cosC + sinC[cosAcosB - sinA sinB]
= sinAcosBcosC + cosAsinBcosC + cosAcosBsinC - sinAsinBsinC

Answer 8

Use the trigonometric identity:
cos(X+Y) = cos(X)cos(Y) - sin(X)sin(Y)

where x can be a and Y can be (b+c)

Answer 9

cos(a + b + c) = cos(a + (b+c)) = cos(a)cos(b+c) - sin(a)sin(b+c)
Use the sum formula to expand cos(b+c) and sin(b+c)

Answer 10

Ohhh Tnks a Lot :D

Answer 11

You are welcome.