If sin x = 3/5 and x is in the second quadrant, what is cos x?

Answer and explanation

Correct answer: C. -4/5

  1. Step 1: sin^2 x + cos^2 x = 1, so cos^2 x = 1 - 9/25 = 16/25. Step 2. cos x = plus or minus 4/5, and in the second quadrant cosine is negative, so cos x = -4/5. Answer: -4/5. Why not the others: 4/5: In the second quadrant cosine is negative. -3/5: That is minus the sine, not the cosine. 5/4: That is the reciprocal.

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