f[r_, b_, x_, m_,
h_] := (r/(m + Cot[x])) (b +
h*Cot[x]) ((b + h*Cot[x])/b)^(m/Cot[x]) - (r/(m + Cot[x]))*b
t[y_] := f[19.2, 0.3, y Degree, 0.529, 1.8]
Solve[D[t[y], y] == 0, y]
\:6B63\:5728\:8BA1\:7B97In[1]:= Solve::ifun: Solve 正在使用反函数，因此可能无法找到某些解；请使用 Reduce 来获取完整的解信息.
Out[3]= {{y -> InverseFunction[
\!\(\*SuperscriptBox[\(f\),
TagBox[
RowBox[{"(",
RowBox[{"0", ",", "0", ",", "1", ",", "0", ",", "0"}], ")"}],
Derivative],
MultilineFunction->None]\), 3, 5][19.2, 0.3, 0, 0.529, 1.8]/\[Degree]}}
In[5]:= {{y -> InverseFunction[
\!\(\*SuperscriptBox[\(f\),
TagBox[
RowBox[{"(",
RowBox[{"0", ",", "0", ",", "1", ",", "0", ",", "0"}], ")"}],
Derivative],
MultilineFunction->None]\), 3, 5][19.2`, 0.3`, 0, 0.529`,
1.8`]/\[Degree]}} // N
Out[5]= {{y -> 57.2958 InverseFunction[
\!\(\*SuperscriptBox[\(f\),
TagBox[
RowBox[{"(",
RowBox[{"0", ",", "0", ",", "1", ",", "0", ",", "0"}], ")"}],
Derivative],
MultilineFunction->None]\), 3, 5][19.2, 0.3, 0., 0.529, 1.8]}}