In triangle RST, RS = 6 cm, ST = 7 cm, and RT = 8 cm. What is the approximate measure of the largest angle in the triangle?

The largest angle is opposite the longest side, RT = 8 cm, so it is angle S. By the law of cosines, cos S = (6² + 7² − 8²)/(2 × 6 × 7) = 21/84 = 0.25, giving S ≈ 75.5°. Thus the largest angle is 75.5°.

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