Hi, I'd be glad to help you with this equation!
The answer is (9)
Hope this helps.
Have a great day!
Angle BAC
cosφ⁻¹ = (10² + 17² - 11²)/(2*10*17) = 37.9 ≈ 38°
Angle ACB
cosφ⁻¹ = (10² + 11² - 17²)/(2*10*11) = 108.0°
Angle ABC
cosφ⁻¹ = (11² + 17² - 10²)/(2*11*17) = 34.0°
See you !
The 2 because we don't know if it is exactly two or if was was rounded up/ down to 2.
