Inequality solving warning: not a valid domain

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1
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I’m trying to solve for inequalities containing multiple parameters about Ishq, but I’m getting warnings. I want to know how to modify codes.

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2

If you carefully look at the documentation for Reduce you should see that it has

Reduce[expression,thingToSolveFor,domain]

In your Reduce above it thinks

0<= VL*Ishp+(1-ksag)*Vs* Sqrt[4*VL^2-3*VL^2*Cos[fai]^2+Ishp^2*ZL^2+ 2*Ishp*VL*ZL*Cos[fai]]/ZL

is your expression and

VL*Ishp+(1-ksag)*Vs* Sqrt[4*VL^2-3*VL^2*Cos[fai]^2+Ishp^2*ZL^2+2*Ishp*VL*ZL*Cos[fai]]/ZL<= VL^2/ZL*Cos[fai]

is the thing you want to solve for and

Ishp

is the domain.

Change your code to put your two expressions inside {} like this

Reduce[{0<= VL*Ishp+(1-ksag)*Vs* Sqrt[4*VL^2-3*VL^2*Cos[fai]^2+Ishp^2*ZL^2+ 2*Ishp*VL*ZL*Cos[fai]]/ZL ,
  VL*Ishp+(1-ksag)*Vs* Sqrt[4*VL^2-3*VL^2*Cos[fai]^2+Ishp^2*ZL^2+ 2*Ishp*VL*ZL*Cos[fai]]/ZL<= VL^2/ZL*Cos[fai]},
  Ishp]

and you avoid this error.