Question
Determine the length of side BC if ∠BAC = 60⁰, AB= 10
cm and AC = 15 cm.Solution
ATQ,
Cos A = (AC² + AB²- BC²) ÷ (2 X AC X AB)
So, cos 60⁰= (15² + 10²- BC²) ÷ (2 X 15 X 10)
OC, (1/2) = (225 + 100 - BC²) ÷ 300
OC, 2 X (325 - BC²) = 300
OC, 325 - BC² = 150
OC, BC² = 175
OC, BC = 5√7 cm
But side cannot be negative.
So, BC = 5√7 cm
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