Quandaries
and Queries
Who is asking: Student
Level: Secondary
Question:
The question is as follows:
"Express sin3A in terms of sinA and cosA."
I can only get work it out so far and then I end up back where I began. Any thoughts or clues to a solution would be greatly appreciated.
Hi,
Write 3A as 2A + A to get
sib3A = sin(2A + A)
and then use the multiple angle expression for the sine.
sin(2A + A) = sin(2A)cos(A) + cos(2A)sin(A)
Now write 2A as A + A
sin(3A) = sin(A + A)cos(A) + cos(A + A)sin(A)
Finally expand sin(A + A) and cos(A + A) using the multiple angle expressions for sine and cosine.
Penny