Find the angle between the planes `vecr.(hati+hatj)=1` and `vecr.(hati+hatk)=3`.

Answer

`pi/3`

Explanation

Given planes are `x+1=1` and `x+z=3`.
The d.r.'s of normals to these planes are `3,-4,5` and `2,-1,-2`.
`therefore costheta=|(1 xx 1)+(1 xx0)+(0xx1)|/(sqrt(1^(2)+1^(2)+0^(2))(sqrt(1^(2)+0^(2)+1^(2))`
`1/(sqrt(2)xx sqrt(2)) =1/2 rArr theta=pi/3`.