gwd-6-9

lingdang1988

in the xy-plane, the point(-2, -3) is the center of a circle. the point ( -2.-1) lies inside the ciecle and the point (4, -3) lies outside the circle. if the radius r of the circle is an integer, then r =

a. 6

b. 5

c. 4

d. 3

e. 2

答案是B。但是我不知道该怎么做？

leadership

LZ的題目錯了~第2個點是（-2，1）而不是（-2，-1）

the point(-2, -3) is the center of a circle. the point ( -2，1) lies inside the ciecle

説明半徑比這兩點閒的距離大，即R>1-（-3）=4

the point(-2, -3) is the center of a circle. the point (4, -3) lies outside the circle

説明半徑比這兩點閒的距離小，即R<4-（-2）=6

所以4<R<6，只能等於5，選B.