cos(x-y) = -1 show that cosx+ cos y=0 and sinx + siny=0

Dear Manoj

cos(x-y) = -1 

that means

x-y = (2n+1)pi

x=y+(2n+1)pi

apply cos on both sides

cos x = cos(y+(2n+1)pi)

=> cosx = -cosy

=> cos x + cos y = 0

in the same way sinx+siny = 0

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Prudhvi Teja