Calculus
posted by j .
determine the angle between the planes 2x + 2y + 7z = 8 and 3x  4y + 4z = 5

let Ø be the angle between their normals
(2,2,7)∘(3,4,4) = √57√41cosØ
cosØ = (6  8 + 28)/(√57√41)
Ø = appr. 57.5°
so the two planes form an angle of 18057.5 or 122.5°