Question

一个圆的面积是原来的8倍,周长增加了50.24,问原来的面积是多少/

Answer 1

S原=∏r^2

S现=∏R^2

S现=8S原

∏R^2=8∏r^2

R^2=8r^2

C原=2∏r

C现=2∏R

C现=C原+50.24

2∏R=2∏r+50.24

R=（2∏r+50.24）/2∏=r+8

R^2=8r^2

(r+8)^2=8r^2

7r^2-16r-64=0

(7r-32)(r+2)=0

r=32/7

这绝对是对的

S原=∏r^2

S现=∏R^2

S现=8S原

∏R^2=8∏r^2

R^2=8r^2

C原=2∏r

C现=2∏R

C现=C原+50.24

2∏R=2∏r+50.24

R=（2∏r+50.24）/2∏=r+8

R^2=8r^2

(r+8)^2=8r^2

7r^2-16r-64=0

(7r-32)(r+2)=0

r=32/7