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Question
If sin A = `12/13`, find sin 3A.
Sum
Solution
If sin A = `12/13`
We know that sin 3A = 3 sin A – 4 sin3 A
`= 3(12/13) - 4(12/13)^3`
`= 12/13 [3 - 4 xx 12/13 xx 12/13]`
`= 12/13 [3 - 576/169]`
`= 12/13[(507 - 576)/169]`
`= 12/13 [(-69)/169]`
`= (- 828)/2197`
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Trigonometric Ratios of Compound Angles
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