BITSAT 2013 Paper

The angle between two planes is the angle between their normals. From the equation of the planes, the normal vectors are

→

N1

= 2

^

i

+

^

j

−2

^

k

and

→

N2

= 3

^

i

−6

^

j

−2

^

k

Therefore, cos θ = |

→ N1 . → N2

| → N1 || → N2 |

|
= = (

4

21

)
Hence, θ = cos−1(

4

21

)