Trigonometric EquationHard
Question
Two adjacent sides of a parallelogram ABCD are given by
and
. The side AD is rotated by an acute angle α in the plane of the parallelogram so that AD becomes AD′. If AD′ makes a right angle with the side AB, then the cosine of the angle α is given by
and
. The side AD is rotated by an acute angle α in the plane of the parallelogram so that AD becomes AD′. If AD′ makes a right angle with the side AB, then the cosine of the angle α is given byOptions
A.

B.

C.

D.

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⇒ cos α = 