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wazhma1991
Mar 15, 2009, 07:05 AM
sin(-2A)=-2sinAcos(-A)

Perito
Mar 16, 2009, 04:42 AM
First, start by proving

sin (x + y) = sin(x) cos(y) + cos(x) sin (y)

sin(x+y) and cos(x+y) (http://www.jimloy.com/geometry/trigz.htm)

Then simplify by letting x = y to the traditional double-angle formula:

Finally, substitute -A for x and you'll have your proof.

wazhma1991
Mar 22, 2009, 04:49 AM
Hi how you solved?:confused:

wazhma1991
Mar 22, 2009, 04:55 AM
Thanks