Find the X3(s) / F(s) using the 3 equations given

Subhotosh Khan

Super Moderator
Staff member
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I have tried to make X1(s) as a subject from equation 1, F(s) from equation 2, and X3(s) from equation 3. I am stuck as I can't get the picture on how to move these three to get the one equation.

Please show us what you have tried and exactly where you are stuck.

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Dr.Peterson

Elite Member
View attachment 29876
I have tried to make X1(s) as a subject from equation 1, F(s) from equation 2, and X3(s) from equation 3. I am stuck as I can't get the picture on how to move these three to get the one equation.

You need to eliminate X1 and X2 from the three equations. One way would be to solve equation 1 for X1 (in terms of X2 and X3) and put that into equations 2 and 3. Now you've eliminated X1 entirely. Then do similarly with the new equations to eliminate X2 as well.

It may help you keep track of things if you temporarily define constants so you can write equation 1 as AX1 = BX2 + CX3, and similarly elsewhere.

iffah

New member

You need to eliminate X1 and X2 from the three equations. One way would be to solve equation 1 for X1 (in terms of X2 and X3) and put that into equations 2 and 3. Now you've eliminated X1 entirely. Then do similarly with the new equations to eliminate X2 as well.

It may help you keep track of things if you temporarily define constants so you can write equation 1 as AX1 = BX2 + CX3, and similarly elsewhere.
I have tried this method, and this is how I get it. Did you mean that I need to make X2 a subject in the equation that I'm currently trying to solve?

Dr.Peterson

Elite Member
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This is what I have done, when I arrive at the third part there are X1 that I have missed. Do I have to insert the X1 into the equation or do I have to change the Third equation and make the X2 as the subject?
If you missed an X1 in the stage where you should have been eliminating it, then you really need to go back and fix that. If you haven't eliminated a variable, then you've accomplished nothing.

In your final equation you still have all three variables, so there has been no progress, and trying to fix that may make it even worse.