Answer:
Angle = 59⁰
Explanation:
First make a sketch of the situation. This results in a triangle.
Now, since there are three sides, the law of cosines is applicable here. This is because we have three sides but unknown angles.
The law of cosines is as follows:
(BC)² = (AB)² + (AC) ² -2AB·AC·Cos A
Making Cos A the subject of the equation gives:
Cos (A) = [(AB)² + (AC)²- (BC)²]/[2AB·AC]
Cos A = [(673)² + (989)² - (861)²]/ (2×673×989)
Cos A = 689 729/ (1331194)
A = Cos⁻¹ [689 729/ (1331194)]
= 58.8⁰
= 59⁰ (nearest degree)