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/

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