Question

Let u = (1, 2 -2), v= (2, 1, 3) and w = j + 4k. a) Find cos theta, where theta is the angle in degrees between u and w.

Answer 1

Answer: The value of cos theta is -0.352.

Step-by-step explanation:

Since we have given that

$\vec{u}=1\hat{i}+2\hat{j}-2\hat{k}\and\\\\\vec{w}=\hat{j}+4\hat{k}$

We need to find the cos theta between u and w.

As we know the formula for angle between two vectors.

$\cos\ \theta=\dfrac{\vec{u}.\vec{w}}{\mid u\mid \mid w\mid}$

So, it becomes,

$\cos \theta=\dfrac{2-8}{\sqrt{1^2+2^2+(-2)^2}\sqrt{1^2+4^2}}\\\\\cos \theta=\dfrac{-6}{\sqrt{17}\sqrt{17}}=\dfrac{-6}{17}=-0.352\\\\\theta=\cos^{-1}(\dfrac{-6}{17})=110.66^\circ$

Hence, the value of cos theta is -0.352.