Use the law of cosines to find the value of 2*4*5 cos theta

a. 20

b. 40

c. - 40

d. 37

my answer is b

We can proceed in solving the problem since all information are given such as 2*4*5costheta.

we have a=4, b=5, and C=theta

let us solve for "c" using Pythagorean

c²=a²+b²

c²=4²+5²

c=6.4

Solving for theta or C

c²=a²+b²-2abcosC

6.4²=4²+5²-2*4*5*cosC

C=90