## University Calculus: Early Transcendentals (3rd Edition)

$1.55$ or $\approx 88.88 ^{\circ}$
The formula to calculate the angle between two planes is: $\theta = \cos ^{-1} (\dfrac{p \cdot q}{|p||q|})$ Here, $u=\lt 0,1,0.2 \gt$ and $v=\lt 1,0,0.1 \gt$ $|u|=\sqrt{(0)^2+(1)^2+(0.2)^2}= \sqrt {1.04}$ and $|v|=\sqrt{(1)^2+(0)^2+(0.1)^2}=\sqrt {1.01}$ Thus, $\theta = \cos ^{-1} (\dfrac{u \cdot v}{|u||v|})=\cos ^{-1} (\dfrac{0.2}{ ( \sqrt {1.04})(\sqrt {1.01}})$ or, $\theta \approx 1.55$ or $\approx 88.88 ^{\circ}$