用绳怎么做降落伞:[3.14*(40+0.02*2)+3.14*(40+0.04*n)]*n/2=50000 求解N等于多少?

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[3.14*(40+0.02*2)+3.14*(40+0.04*n)]*n/2=50000 求解N等于多少?

[3.14*(40+0.02*2)+3.14*(40+0.04*n)]*n/2=50000
[3.14*40.04+3.14*40+3.14*0.04n]*n=100000
[3.14*80.04+3.14*0.04n]n=100000
0.1256n^2+251.3256n=100000
n^2+2001n=796178.34
[n+1000.5]^2=1797178.59
n+1000.5=+/-1340.5

n=340
或者
n=2341

2341