Question

The line segment with endpoints (−20, 21) and (0, 0) is graphed on the standard coordinate plane and makes an angle, Θ, with respect to the x axis. What is cos Θ? A) − 20 29 B) − 29 20 C) − 20 21 D) 21 29

Answer 1

see the attached figure to better understand the problem
Let
A (−20, 21)
B (0, 0)

step 1
find the distance AB
d=√[(y2-y1)²+(x2-x1)²]------> d=√[(0-21)²+(0+20)²]
d=√841------> d=29 units

step 2
find cos ∅

cos ∅=adjacent side angle ∅ /hypotenuse
adjacent side angle ∅=20 units
hypotenuse=distance AB=29 units
so
cos ∅=-20/29-----> is negative because ∅ belong to the II quadrant

the answer is
cos ∅=-20/29