Which two angles are both coterminal with Ø= 90 degrees?

Question

_{a) 270 and -90}

b) 270 and 450

c) 0 and 180

d) 450 and -270

Answer 1

The term "coterminal" means that our terminal side of our angles match:

The best way to visualize is to take an x-y graph and place a pencil along the X-axis. The X-axis will be the initial side of our angle. From here, rotate the pencil 90 degrees counterclockwise: This will be our terminal side, and the side we will try and match.
Starting with
A: 270 and -90
 270 will pass 90 degrees, so we know this answer can be eliminated.
B:270 and 450
 270 again will pass 90 degrees, so we know this answer can be eliminated.
C:0 will remain at the initial side, so this answer can be eliminated, which leaves:

D: 450 and -270
with 450, we subtract 360 to get 90, which will satisfy the coterminal angles.
For -270, we rotate the pencil to the RIGHT 270 degrees, which will terminate on the 90 degree line, making this satisfy the coterminal angle as well!