00:01
So in this question, they say without using a calculator, i want to compute the sine and cosine of 315 degrees by using the reference angle.
00:14
So in order to do this, i need to know where is 315 degrees? well, remember that 0 degrees points along the positive x -axis.
00:30
Then 90 degrees is along the positive y axis, 180 degrees is along the negative x axis, 270 degrees is along the negative y axis, and then 360 degrees brings you back to the positive x axis.
00:58
And so 315 degrees is exactly halfway between 270 and 360.
01:07
It's 45 more than 270 and 45 less than 360.
01:14
So here is my 315 degree angle.
01:20
Now, my reference angle is the angle made with the x -axis, the acute angle with the x -axis.
01:30
This is going to be a 45 -degree angle.
01:33
It's in the middle of this fourth quadrant.
01:36
So my reference angle is 45 degrees, and this angle is in quadrant 4...