with these identities

a. sin(-x) = -sinx

b. cos(-x) = cos(x)

c. cos(x+y) = cosxcosy - sinxsiny

d. sin(x+y) = sinxcosy + cosxsiny

i need to derive this

sin^2x + cos^2x = 1

can anyone help me

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- Sep 1st 2008, 08:37 AMCraig is Legendderving trig equations
with these identities

a. sin(-x) = -sinx

b. cos(-x) = cos(x)

c. cos(x+y) = cosxcosy - sinxsiny

d. sin(x+y) = sinxcosy + cosxsiny

i need to derive this

sin^2x + cos^2x = 1

can anyone help me - Sep 1st 2008, 08:44 AMPlato
With the following can you complete it?

$\displaystyle 1 = \cos (0) = \cos \left( {x + ( - x)} \right) = \cos (x)\cos ( - x) - \sin (x)\sin ( - x)$