Clear["Global`*"];Subscript[q, r] =
Q - (Subscript[p, r] - Subscript[p, e])/(1 - \[Theta]);Subscript[q,
e] = (\[Theta] Subscript[p, r] - Subscript[p,
e])/(\[Theta] (1 - \[Theta]));Subscript[\[Pi], m] =
w Subscript[q, r] +
Subscript[p, e] Subscript[q,
e] - (c - Subscript[o, 2] l) (Subscript[q, r] + Subscript[q, e]);
Subscript[\[Pi],
r] = (Subscript[p, r] - w) Subscript[q, r] +
Subscript[o, 1] l (Subscript[q, r] + Subscript[q, e]) - kl^2;
FullSimplify[
Solve[D[Subscript[\[Pi], r], Subscript[p, r]] == 0, Subscript[p, r]]]

可以处结果啊。方程有点复杂，可以用FullSimplify将Subscript[\[Pi],
r] 转为traditional form 看一下，结果为：
Subscript[p, r] -> 1/2 (Q + w - Q \[Theta] + Subscript[p, e])

好的谢谢～可以出结果了
但是下一步结果又出不来了，可以再请您看一下吗？
Clear["Global`*"];
Subscript[q, r] =
Q - (Subscript[p, r] - Subscript[p, e])/(1 - \[Theta]);
Subscript[q,
e] = (\[Theta] Subscript[p, r] - Subscript[p,
e])/(\[Theta] (1 - \[Theta]));
Subscript[\[Pi], m] =
w Subscript[q, r] +
Subscript[p, e] Subscript[q,
e] - (c - Subscript[o, 2] l) (Subscript[q, r] + Subscript[q, e]);
Subscript[\[Pi],
r] = (Subscript[p, r] - w) Subscript[q, r] +
Subscript[o, 1] l (Subscript[q, r] + Subscript[q, e]) - kl^2;
FullSimplify[
Solve[D[Subscript[\[Pi], r], Subscript[p, r]] == 0, Subscript[p, r]]]
FullSimplify[Solve[D[Subscript[\[Pi], r], l] == 0, l]]

应该是下标问题，直接Solve[\[PartialD]Subscript[\[Pi], r]/\[PartialD]l == 0, l]会出现以下错误。
Subscript[\[Pi], r] cannot be interpreted. A partial derivative requires a subscript differentiation variable.
查了一下。应该是软件不理解你的语句，虽然你理解。新手是不建议用Subscript的，会造成误解。你可以去网上查找，有不少建议！

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