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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With the following can you complete it? $\displaystyle 1 = \cos (0) = \cos \left( {x + ( - x)} \right) = \cos (x)\cos ( - x) - \sin (x)\sin ( - x)$
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