9
QuizMultiple Choice

Trigonometric Double Angle Identities — Quiz

Question 9 • Precalculus

If tangent of x is equal to 3 fifths and sine of x is greater than 0 , what is sine of 2 x ?

Answer
A
the fraction with numerator 3 and denominator square root of 34
B
the fraction with numerator 6 and denominator square root of 34
C
30 over 34
D
9 over 34

Explanation

Use the double-angle identity: sin(2x) = 2 tan(x) / (1 + tan²(x)). Substituting tan(x) = 3/5 gives sin(2x) = 2(3/5) / (1 + 9/25) = (6/5) / (34/25) = 30/34. Thus the answer is 30 over 34. The condition sin(x) > 0 is consistent with the positive tangent, but the identity already determines the result.

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