Question

find the value of cos (90 +theta) ​

Answer 1

-sinx

Explanation:

let theta = x

x+90 lies in 2nd quadrant

base is negative in second quadrant

so the value of cos will be negative

as 90 degree lies on complementary line it will changed in sin ratio

hence cos (90+x) = (-sinx)

Answer 2

Cos(90+theta) = -sin theta

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