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Trigonometrical Ratios of Standard Angles [Including Evaluation of an Expression Involving Trigonometric Ratios] — MATHEMATICS STD 9 — Question

ICSE BoardEnglish MediumSTD 9MATHEMATICSTrigonometrical Ratios of Standard Angles [Including Evaluation of an Expression Involving Trigonometric Ratios]2 Marks
Question
Solve for $x : 2 \cos (3x - 15^\circ ) = 1$
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Answer

$2 \cos(3x –15^\circ ) = 1$
$\cos (3x – 15^\circ ) = \frac{1}{2}$
$\cos (3x – 15^\circ ) = \cos 60^\circ $
$3x – 15^\circ = 60^\circ $
$3x = 75^\circ $
$x = 25^\circ $

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