Trigonometric EquationHard

Question

ABCD is a cyclic quadrilateral then the value of cos A + cos B + cos C + cos D

Options

A.0
B.1
C.2(cos A + cos B)
D.None of these

Solution

In cyclic quadrilatral   ∠A + ∠C = 180o
and                            ∠B + ∠D = 180o
cos(180 - C) + cos(180 - D) + cos C + cos D
= - cos C - cos D + cos C + cos D = 0

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