Suppose that 0degrees<theta<180degrees. what is the sign of each of the following?
a) cos theta/2
b)sin(-theta)
4 answers
cos theta/2 is positive and sin(-theta) is negative
How do you know by looking at them?
Sketch a graph
If theta is between 0 and 180 then theta/2 is between 0 and 90. Therefore in the first quadrant.
In the first quadrant, all trig functions are positive.
If theta is between 0 and 180 then negative theta is between 180 and 360 in the lower two quadrants, quadrants 3 and 4. In those quadrants y is negative so sin theta is negative.
If theta is between 0 and 180 then theta/2 is between 0 and 90. Therefore in the first quadrant.
In the first quadrant, all trig functions are positive.
If theta is between 0 and 180 then negative theta is between 180 and 360 in the lower two quadrants, quadrants 3 and 4. In those quadrants y is negative so sin theta is negative.
oh okay! I get it now, thanks!:)