Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 1 - No. 50)
If two sides of a triangle are 7 cm and 9 cm, and the included angle is 60 degrees, what is the length of the third side (approximately)?
7.07 cm
8.00 cm
8.2 cm
9.0 cm
Explanation
Use the cosine rule: c² = 7² + 9² - 2 * 7 * 9 * cos(60). c ≈ 8.08
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