Got a question with substitution?

[MRAI]

Using the Substitution method, find the maximum value of

 

4x-2xy+3y subject to the constraint 4x-y=2

 

I can do the 1st part:

 

4x-y=2--->

4x-2=y

 

substitute this into the original equation:

4x-2x(4x-2)+3(4x-2)

 

Hope that right so far! but dont know where to go from there? any one could help plz?

 

thanks :)

[zephyrus17]

I really advise you to check your textbook. Try on your own first, then, if you still can't solve it, check with a friend or consult your Mathematics teacher. :)

[maddog]

I really advise you to check your textbook. Try on your own first, then, if you still can't solve it, check with a friend or consult your Mathematics teacher. :)

The substitution does look right. However something fundamental seems missing.

For example, what is the following formula equal ?

 

4x - 2xy + 3y = ?

 

If the ? is 0, then solve what you have for x, you will then have what x equals.

Plug that back in the original equation and solve for y. Voila! You have your answer.

 

maddog