Hi;
Need help with reference angles... I know the cos of 150degrees and the cos of 30degrees are the same ie sqrt3 /2 but with a sign change.
I know they lie in the same quadrant but that all I know and I need to be able to prove it.
Thanks
Hi;
Need help with reference angles... I know the cos of 150degrees and the cos of 30degrees are the same ie sqrt3 /2 but with a sign change.
I know they lie in the same quadrant but that all I know and I need to be able to prove it.
Thanks
Unfortunately, what you say you "know" is wrong. "150 degrees" lies between 90 and 180 so is in the second quadrant while 30 degrees is between 0 and 90 degrees and, like any "reference angle", is in the first quadrant. Are you clear on what "quadrant" means here? Representing points on a unit circle, in an xy-coordinate system, the "quadrants" are the four parts into which the x and y axes divide the plane. The "first quadrant" is the upper right, between 0 and 90 degrees where x and y are both positive. Since "sine" is the y coordinate on the unit circle and "cosine" is the x coordinate, they are both positive in the first quadrant. The "second quadrant" is the upper left, between 90 and 180 degrees where x is negative and y is positive- sine is still positive but now cosine is negative. The "third quadrant" is the lower left, between 180 and 270 degrees where x and y are both negative so sine and cosine are both negative. Finally, the "fourth quadrant" is the lower right, between 270 and 360 degrees where x is positive and y is negative. Cosine is positive and sine is negative. As you go through the four quadrants, from first to fourth, sine goes "+,+,-,-" while cosine goes "+,-,-,+".