RRB Group D 22-Sep-2018 Shift 1 Solved Paper

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Question : 25 of 100

Marks: +1, -0

If

3\cos^{2} x-2 \sin ^{2} x=-0.75

and

0° ≤ x \≤ 90°

then

x=

$45°$
$60°$
$30°$
$90°$

Solution:

3 \cos ^{2} x-2 \sin ^{2} x=-0.75

3(1-\sin ^{2} x)-2 \sin ^{2} x=-0.75

3-5 \sin ^{2} x=-0.75

5 \sin ^{2} x=3.75

\sin x=\√{.75}

\sin x=0.866={\√{3}}/{2}

\⇒x=60°

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