Question

Use the law of cosines to find the value of 2 x 2 x 2 cos(theta).

***see picture attached inside!!**

A. 7

B. -7

C. -8

D. 8

***do not understand at all! :( pls explain! Thanks!! :)

Answer 1

the side opposite theta is 1

so this means

c^2 = a^2 + b^2 - 2abcos(C)

1^2 = 2^2 + 2^2 - 2*2*2cos(theta)

now isolate the expression "2*2*2cos(theta)"

Answer 2

eek! this is where i'm lost :( how do i isolate it? :/

Answer 3

think of it as 'x'

1^2 = 2^2 + 2^2 - 2*2*2cos(theta)

1^2 = 2^2 + 2^2 - x

solve for x

then replace x with 2*2*2cos(theta) after you've solved for x

Answer 4

so x=7 ?

Answer 5

ohhh so my answer is A. 7 ?? :O is that right? :)

Answer 6

yep

Answer 7

yay! thanks! :)