Question

Proof cos 90 plus theta is equal to minus sin theta

Answer 1

cos90+ theta

we know that only sin and cosec lies in second quadrant and 90 + theta also lies second quadrant , here only the value of sin and cosec will be positive otherwise the value of all trigo ratio is negative .and at 90+theta and at 270+theta , all trigo becomes inverse and hence cos 90 + theta = -sin theta.

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Answer 2

Answer:

Since angle 90+ will lie in the second quadrant

and the second is for Sin and Cosec

so if we calculate for Cos

it gives negative value

$\ \cos(90 + x) = - sin(x)$