[問題]天山數學9-8

[mark-alan]

A thin piece of wire 40 meters long is cut into two pieces. One piece is used to form acircle with radius r, and the other is used to form a square. No wire is left over. Whichof the following represents the total area, in square meters, of the circular and the square
regions in terms of r?

A. pai r^2
B. pai r^2 + 10
C. pai r^2 + ? pai^2r^2
D. pai r^2 + (40-2pai r)^2
E. pai r^2 + (10- ? pai r)^2

我算D 答案E...-.-"

[汪汪北鼻]

X=2paiR

square 邊長=(40-X)/4=(40-2paiR)/4

thus, the sum of the area of the circular and the square
regions in terms of r?

paiR^2+[(40-2paiR)/4}^2=E

[mark-alan]

我知道為啥我算D了....
我把長方形周長當"邊長".....
我要粗心大意到幾時啊.......