First of all i think that r3 is shorted too.

By what R3 is shorted?

Yhen vin is I*Rin but in order to vanish the vgs term in the numerator i need that vgs will conclude in the vin term.so how i add the Rin to the buisness.understand?

But in your circuit, I do not seee any signal source resistance hence the Vin = Vgs.

 

I need help in 2 things. Dc analyze Vthevenin and Rthevenin.becuase of the fact ig=0 the Vthevenin is voltage between R2 and R3 .how i calculate that.and is the Rthevenin is (R1+R2)||R3?
Now in ac analyze is the Rin= R1+R2||R3?
Much regards for answering

 

Anyone help please

 

Dc analyze Vthevenin and Rthevenin.becuase of the fact ig=0 the Vthevenin is voltage between R2 and R3 .how i calculate that

Apply voltage divider equation and solve for the voltage across R3 resistor.

and is the Rthevenin is (R1+R2)||R3?

For DC yes.

Now in ac analyze is the Rin= R1+R2||R3?

No, wrong. If we ignore Q2 then Rin = R1||(R2+R3)