So the distance formula is [tex] \sqrt{(x_2-x_1)^2+(y_2-y_1)^2} [/tex] . Using this, our equation is [tex] \sqrt{(7-(-8))^2+(-1-(-9))^2} [/tex] and we can solve for it as such:
[tex] \sqrt{(7-(-8))^2+(-1-(-9))^2}\\ \sqrt{15^2+8^2} [/tex]
As we see with this radical, the sum that's under it is 15^2 + 8^2, or the third option.
