Chapter 12: Vectors and the Geometry of Space - Section 12.5 - Lines and Planes in Space - Exercises 12.5 - Page 727: 52

$ 0.73$

The angle between two plane is given by: $ \theta = \cos ^{-1} (\dfrac{a \cdot b}{|a||b|})$ Here, $a=\lt 0,4,3 \gt$ and $b=\lt 3,2,6 \gt$ $|a|=\sqrt{0^2+4^2+3^2}= 5$ and $|b|=\sqrt{3^2+2^2+6^2}= 7$ Now, $ \theta =\cos ^{-1} (\dfrac{26}{ 35})$ Thus, $ \theta = 0.73$ rad