Respuesta :

Rearrange the formula to get cos(A) = (b^2 + c^2 - a^2) / (2bc)
cos(X) = (20^2 + 18^2 - 22^2) / (2 x 20 x 18) = 0.33333...
X = cos^-1(0.3333...) = 70.5 degrees (1 dp)