Angles between planes?!

Question

Q1) Find the angle between the planes

-1x - 1y + 3z = 2

and

-2x - 4y + 3z = 2

in radians to at least 8 significant figures

Expected to answer this but havent even gone over it in class so working would be greatly appreciated thank you :)

Answer 1

Given planes are  .

The normal vectors for the planes are .

Consequently the angle between the two planes is cosine of angle between .

i.e, 

⇒ θ = 32.874⁰ = 32.874 * (π/180) radians

.

Therefore, the angle between the given two planes is 0.57377 radians.