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Answer:
cos(A) ≈ 0.9165
Step-by-step explanation:
Put the given value into the given relation and solve for the unknown.
sin²(A) +cos²(A) = 1
(2/5)² + cos²(A) = 1
cos²(A) = 1 -4/25 = 21/25 . . . . . subtract (2/5)²
cos(A) = √(21/25) ≈ 0.9165 . . . . . take the square root
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Both sine and cosine are positive in Quadrant I, so we're only interested in the positive square root.
