First you solve 2y-3y=9.

Now that you have y, then you substitute y into x-2y=3 to find X

Your solution is (-15, -9)
Answer: 1
13pi/2 can be simplified onto 6 pi/2, so it goes around the unit circle 6 times and left with pi/2. the coordinates of pi/2 is (0,1). the trigonometric function sin is y/r. since r is always 1 on the unit circle, the answer is the y value, in this case it is 1.
There is no positive or negative correlation
*I'll be keeping the solutions in exact form*
So firstly, square root both sides. This will split the equation into two:

Next, add 1 on each side: 
Next, divide 3 on both sides, and your answers will be 