Question

The sign of the value of cos 112.5º is _____??

Answer 1

do you need the answer of cos 112.5?

Answer 2

You don't even need to get a calculator out. Just visualize a coordinate plane. In which quadrant does 112.5 degree lie in? Remember it's bigger than 90 degrees and smaller than 180 degrees.

Answer 3

I'm sorry, i'm not sure then! I know how to find it though.

Answer 4

that's all the question says. i think you have to use half-angle identities?

Answer 5

So 112.5 degrees lie in the 2nd quadrant.
Since x-coordinate of the point where the angle meets the unit circle is negative, the cosine of 112.5 is negative.

Answer 6

oh ok thank you so much! and thanks for drawing out the triangle

Answer 7

You're welcome. :D