If cos 3 A -0 and A is acute - find the value ofi sin A ii cos 2 AA- i 1-2 ii -2- B- i 30- ii 60- -C- i 1-2 ii 1-2D- i 1-3 ii -3

The correct option is C (i) 1/2 (ii) 1/2 Given the cos 3 A = 0 We know cos 90° = 0 ∴ cos 3A = cos 90° 3A = 90° ...

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Standard IX

Mathematics

Opposite & Adjacent Sides in a Right Angled Triangle

If cos 3 A =0...

Question

If cos 3A = 0 and A is acute , find the value of

(i) sin A (ii) cos 2A

(i) $\frac{1}{2}$ (ii) $\frac{1}{2}$

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( i) $\frac{1}{\sqrt{3}}$ (ii) $\sqrt{3}$

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(i) 30° (ii) 60°

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(i) $\frac{1}{\sqrt{2}}$ (ii) $\sqrt{2}$

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Solution

The correct option is A
(i) $\frac{1}{2}$ (ii) $\frac{1}{2}$

Given the cos 3 A = 0

We know cos 90° = 0

$∴$ cos 3A = cos 90°

3A = 90°

A = 30°

(i) sin A = sin 30° = $\frac{1}{2}$

(ii) cos 2A = cos 2(30°) = cos 60° = $\frac{1}{2}$

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If cos 3A = 0 and A is acute , find the value of (i) sin A (ii) cos 2A

The correct option is A (i) 12 (ii) 12 Given the cos 3 A = 0 We know cos 90° = 0 ∴ cos 3A = cos 90° 3A = 90° A = 30° (i) sin A = sin 30° = 12 (ii) cos 2A = cos 2(30°) = cos 60° = 12

If cos 3A = 0 and A is acute , find the value of

(i) sin A (ii) cos 2A

The correct option is A
(i) $\frac{1}{2}$ (ii) $\frac{1}{2}$

Given the cos 3 A = 0

We know cos 90° = 0

$∴$ cos 3A = cos 90°

3A = 90°

A = 30°

(i) sin A = sin 30° = $\frac{1}{2}$

(ii) cos 2A = cos 2(30°) = cos 60° = $\frac{1}{2}$