Prove the following by using Trigonometrical Ratios of Standard Angles
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Hope it will help you
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adithya02:
but the question says to prove using trigonometric ratios of standard angles
so i think u need to assume a theta value then evaluate it
like how i did in my answer
don't apply so much of brain when you don't have 'em
i am applying so much of brain coz i have them more than you
X D
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the actual way to solve is
cosθ (sin 90-θ) + sinθ cos(90-θ)
= cosθ *cosθ + sinθ * sinθ (using identity cosA = sin(90-A) and sinA = cos(90-A))
= cos^2θ + sin^2θ
= 1
but since they asked to prove using angles
take θ = 30
cos30 * sin (90-30) + sin30 * cos(90-30)
= cos30sin60 + sin30cos60
= (root3/2 * root3/2) + (1/2 * 1/2)
= 3/4 + 1/4 = 1. Hence proved
cosθ (sin 90-θ) + sinθ cos(90-θ)
= cosθ *cosθ + sinθ * sinθ (using identity cosA = sin(90-A) and sinA = cos(90-A))
= cos^2θ + sin^2θ
= 1
but since they asked to prove using angles
take θ = 30
cos30 * sin (90-30) + sin30 * cos(90-30)
= cos30sin60 + sin30cos60
= (root3/2 * root3/2) + (1/2 * 1/2)
= 3/4 + 1/4 = 1. Hence proved
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