# Trigonometric Ratios Of Complementary Angles

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Two angles are said to be complementary if the sum of their angles is 90^{o}. In triangle ABC, the pair of complementary angles are

So ∠A + ∠B = 90^{o}

sin A =

Let us now define trigonometric ratios for angle B in terms of it's complementary angle.

B = 90^{o} - A

So sin B = sin(90 - A) =

cos C = cos (90-A) =

tan C = tan (90-A) =

sin(90-A) = cos A cosec(90-A) = sec A

cos(90-A) = sin A sec(90-A) = cosec A

tan(90-A) = cot A cot(90-A) = tan A

**Note :** tan 0° = 0 = cot 90°, sec 0° = 1 = cosec 90° and sec 90°, cosec 0°, tan 90° and cot 0° are not defined.