gwd math 11-21

greatvampires

这一题有一点不明白的是，为什麽只知道半径就可以知道答案呢？哪位可

以执教一二？

Q21:

A certain circle in the xy-plane has its center at the origin. 

If P is a point on the circle, what is the sum of the squares of

the coordinates of P?

(1)     The radius of the circle is 4.

(2)     The sum of the coordinates of P is 0.

lizhihuantu

它问的是P的坐标的平方和，圆心在原点的圆的方程是x^2+y^2=r^2 ,知道半径就是知道平方和喽.

greatvampires

谢谢楼主！！！！！