solve xy-3x=40 for y, find value for x=5; solve 7x-xy=-18,

[christina520]

1. solve the equation for y, then find value of y for given value of x. : xy - 3x = 40 ; x=5

and, also:

2. solve the equation for y, then find value of y for given value of x. : 7x - xy = -18 ; x=-4

I'm having trouble getting the y by itself. In the instructions my teacher gave me, it says to do distrubute, but that would just have the x alone. :/

 

[stapel]

solve the equation for y, then find value of y for given value of x. : xy - 3x = 40 ; x=5

Would you be able to solve 3y - 9 = 40 for y? If so, then follow the same steps here. The only difference is that you will not be able to simplify as much, as you work through the steps. :wink:

If you get stuck, please reply showing how far you have gotten. Thank you!

Eliz.

 

[christina520]

Re: Solve the equation for y

xy - 3x = 40
xy + 3x = +3x
xy = 40 + 3x
xy/x = 40/x + 3x/x
y= 40/x + 3

???????

 

[mmm4444bot]

Re: Solve the equation for y

Hi Christina:

You wrote,

... y= 40/x + 3

???????

Thank you for showing us your work, but is ??????? supposed to be some sort of question?

I have to guess why you stopped at this point.

Did you forget the instructions? You're trying to find the value of y when x = 5. Your work shows that you discovered an expression for y.

y = (40/x) + 3

In order to find the value of y when x = 5, you need to replace the symbol x with the number 5 and do the arithmetic to get a number.

I look forward to seeing your work on the other problem.

Please feel free to ask specific questions if there is something that you do not understand.

~ Mark