# Double Angle Formula

• Apr 27th 2009, 01:40 PM
jumpman23
Double Angle Formula
Find the exact value of sin2x.

Sinx = (-4/7)
• Apr 27th 2009, 01:44 PM
Jameson
Quote:

Originally Posted by jumpman23
Find the exact value of sin2x.

Sinx = (-4/7)

You should know from class that $\sin(2x)=2\sin(x)\cos(x)$. You already known sin(x). To find cos(x) you can use the info already given to draw a right triangle and solve for the missing leg needed to find cos(x).