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JEE Previous Year Question

$If a = 2, b = 3, c = 4 in a triangle ABC, then cos C =$

Topic: JEE PYQ

Answer: B. Full step-by-step solution below.

A $\frac{1}{4}$
B $\frac{- 1}{4}$
C $\frac{1}{2}$
D $\frac{- 1}{2}$

Correct answer: B

Solution

(b) cos C = \frac{a ^{2} + b ^{2} - c ^{2}}{2 ab} = \frac{( 2 ) ^{2} + ( 3 ) ^{2} - ( 4 ) ^{2}}{2 ( 2 ) ( 3 )} = \frac{- 1}{4}

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