M = 1; c = 0.5; a = 0.5; Q = 0.6; L = 10; q = 10;Subscript[A, t1] = 2 a^2 (M - r) + ( Q (a^2 + c^2 - r^2))/(a^2 + c^2 + r^2)^2; Subscript[A, L] = -(( Q*r*a)/(r^2 + c^2)); Subscript[A, L1] = ( a Q (-c^2 + r^2))/(c^2 + r^2)^2;F = ((r^2 + c^2)*(r^2 - 2 M*r - c^2 + a^2 + Q^2))/((r^2 + a^2 + c^2)^2 - a^2*(r^2 - 2 M*r - c^2 + a^2 + Q^2)); Subscript[F, 1] = -((2 (a^4 (c^2 (M - 2 r) + r (Q^2 - M r)) + (c^2 + r^2)^2 (c^2 (M - 2 r) + r (Q^2 - M r)) + a^2 (2 c^4 M - 2 c^2 r (Q^2 + 2 r (-2 M + r)) + r (Q^4 + 2 M (2 M - r) r^2 + 2 Q^2 r (-2 M + r)))))/((c^2 + r^2)^2 + a^2 (3 c^2 - Q^2 + 2 M r + r^2))^2);d = ((r^2 + a^2 + c^2)^2 - (r^2 - 2 M*r - c^2 + a^2 + Q^2) a^2)/( r^2 + c^2);Subscript[d, 1] = 2 (r + (a^2 (c^2 (M - 2 r) + r (Q^2 - M r)))/(c^2 + r^2)^2);f[r_] = -q*Subscript[A, t1] - (Subscript[F, 1] + (L + q*Subscript[A, L])*(2 q*Subscript[A, L1]*d^-1* F - (L + q*Subscript[A, L]) d^-2*Subscript[d, 1]* F + (L + q*Subscript[A, L]) d^-1*Subscript[F, 1]))/( 2 Sqrt[F*(1 + (L + q*Subscript[A, L])^2 d^-1)]);Plot[f[r], {r, 0, 10}, PlotRange -> {-1, 1}]ans = NSolve[f[r] == 0] 求助 为什么L=8的时候这个函数在（1-2）之间有实数解，L=10的时候没有实数解，但是作图出来又是能够看见1-2之间是存在点的。