Solve these simultaneous equations. x^2+y^2=9, x-y+3=0

Rearrage so you have x+3=y, and x² +y² =9. Substitute the equation into another so you have x²+(x+3)²=9. Expand the brackets so that you have  x²+x²+6x+9=9. Then you rearrange so it's all on one side of the equation and equal to zero you will then have 2x²+6x=0 you can the divide by two so you have x²+3x=0. You then have to factorise so you have x(x+3)=0. This means you now know the value of x, it is either -3 or 0. You then substitute those values int either one of the two equations (usually the easier one) so you now have y=3 when x=0 and y=0 when x=-3.