• p = 8 cm
    q = 10 cm
    ∠R = 60°
    r² = p² + q² - 2pq×cos∠R
    r² = 8² + 10² - 2×8×10×cos 60°
    r² = 64 + 100 -160×1/2
    r² = 164-80
    r² = 84
    r = √84
    r = 2√21 cm

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