NDA 2023 Maths · Mathematics · Properties of Triangles · medium

The cosine of its largest angle is

Single correct option

The sides of a triangle are

4

5

and

6

. The cosine of its largest angle is

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Answer: (C) $\dfrac18$

The largest angle is opposite the longest side

6

. By the cosine rule

\cos C=\dfrac{4^2+5^2-6^2}{2\cdot4\cdot5}=\dfrac{5}{40}=\dfrac18

. The options

\tfrac34

and

\tfrac9{16}

are

\cos A

and

\cos B

for the angles opposite sides

4

and

5

respectively.

Original question written in the NDA 2023 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake