Use Laws of cosine to solve the triangle given that a 6 b

Use Laws of cosine to solve the triangle given that a = 6, b = 9, c = 12.

Solution

a =6 , b =9 , c =12

Use law of cosine to find angles:

cosA = (b^2 +c^2 - a^2)/(2bc)

= (9^2 +12^2 -6^2 )/(2*6*9)

A= 28.96deg

again apply cosine rule to find angle B

cosB = (a^2 +c^2 -b^2)/2ac

=(6^2 +12^2 -9^2)/(2*6*12)

B = 46.47 deg

Angle C = 180 -A -B = 104.57 deg