[tex]1) \\ \\ x^2+y^2=4\\\\Circle \ whose \ center \ is \ at \ the \ origin. \\Circle \ with c\ enter (0,0),\\ radius : \ r^2=4 \\r= \sqrt{2}\\r=2[/tex]
[tex]2)\\y=3x+9\\ x=-3\ \to\ y=3\cdot (-3)+9=-9+9=0\\x=0\ \to\ y=3\cdot 0+9=9 \\\\3) \\x+y=10\\y=-x+10 \\ x=0\ \to\ y=-0+10=10 \\ x=10\ \to\ y=-10+10=0[/tex]
