Given that sine theta is equal to 21 over 29 , what is the value of cosine theta , for 0 degrees is less than theta comma theta is less than 90 degrees ?

Use the identity sin²θ + cos²θ = 1. Since sin θ = 21/29, cos²θ = 1 − (21/29)² = (841 − 441)/841 = 400/841, so cos θ = ±20/29. Because θ is between 0° and 90°, its cosine is positive. The answer is 20/29, choice D.

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