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fairy3636

铁虫 (小有名气)

[求助] solve函数解方程得出的解是错误的,是软件算错了吗?

syms r_2 d_1 d_2 d_3 f_SYS

eq=sym('- (d_3 - f_SYS)/f_SYS - ((f_SYS*(4*f_SYS*d_1^2*d_2^2 - 2*d_1*d_2*r_2^3 + 4*f_SYS*d_1*d_2*r_2^2 + d_1*r_2^4 - d_2*r_2^4))^(1/2) - 2*d_1*d_2*f_SYS)/(f_SYS*r_2^2)=0');

solve(eq,'r_2');

运行后,得出r_2的两个解:

  ((d_1*d_2*f_SYS*(4*d_3*f_SYS^2 - 8*d_3^2*f_SYS + 4*d_3^3 + d_1*d_2*f_SYS - 4*d_1*d_3*f_SYS + 4*d_2*d_3*f_SYS))^(1/2) - d_1*d_2*f_SYS)/(d_2*f_SYS - d_1*f_SYS - 2*d_3*f_SYS + d_3^2 + f_SYS^2)

-((d_1*d_2*f_SYS*(4*d_3*f_SYS^2 - 8*d_3^2*f_SYS + 4*d_3^3 + d_1*d_2*f_SYS - 4*d_1*d_3*f_SYS + 4*d_2*d_3*f_SYS))^(1/2) + d_1*d_2*f_SYS)/(d_2*f_SYS - d_1*f_SYS - 2*d_3*f_SYS + d_3^2 + f_SYS^2)


第一个解是正确的;但第二个解是错误的,代入原方程不成立!

奇怪的是,如果把方程中d_1 d_2 d_3 f_SYS赋值,比如:d_1=-1700;d_2=1700;d_3=-1700;f_SYS=-5000;

则方程eq='((17000000*r_2^4 - 28900000000*r_2^3 - 289000000000000*r_2^2 + 835210000000000000000)^(1/2) - 28900000000)/(5000*r_2^2) + 33/50=0'

这时方程仅计算出一个解:  -2.2907e+03

不知道出现上述情况是什么原因,大家帮忙看看。
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