Answer:
see explanation
Step-by-step explanation:
Using the Cosine rule
a² = b² + c² - 2abcosA ← Rearranging for cosA gives
cosA = [tex]\frac{b^2+c^2-a^2}{2ab}[/tex]
(a)
let a = 10, b = 7, c = 8 and A = α, then
cosα = [tex]\frac{7^2+8^2-10^2}{2(7)(8)}[/tex] = [tex]\frac{49+64-100}{112}[/tex] = [tex]\frac{13}{112}[/tex], thus
α = [tex]cos^{-1}[/tex]( [tex]\frac{13}{112}[/tex] ) ≈ 83° ( to the nearest degree )
(b)
let the angle opposite side 7 be x
Using the Sine rule
[tex]\frac{10}{sin83}[/tex] = [tex]\frac{7}{sinx}[/tex] ( cross- multiply )
10sinx = 7sin83 ( divide both sides by 10 )
sinx = [tex]\frac{7sin83}{10}[/tex] , thus
x = [tex]sin^{-1}[/tex] ( [tex]\frac{7sin83}{10}[/tex] ) = 44°
The third angle can be found using the sum of angles in a triangle
third angle = 180° - (83 + 44)° = 180° - 127° = 53°
The 3 angles are 83°, 44°, 53°
