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mathshelp · Apr 29, 2009, 07:26 AM

I have two questions that I am having trouble with, I don't so much want the answers but the method of how to work them out:

Transpose these equations to make the 'y' the subject.

(1) 7(6-3y) + 5(2y+4) = 4x+9

(2) 4x/3 +1 = 3y/2 - 6

Were ' / ' means divide.

Perito · Apr 29, 2009, 07:33 AM

1.
a. Multiply out the expressions, 7(6-3y) and 5(2y+4).
b. collect like terms (add/subtract constants, add coefficients of y
c. Subtract the constant from both sides.
c. Solve the equation for y by dividing by the coefficient of y.

2.
a. multiply both sides of the equation by 6 (to get rid of the denominators).
b. Add a constant (36) to both sides of the equation.
c. Divide both sides of the equation by the coefficient of y. That will solve for y in terms of x
(I think that's what it means to make "y" the subject, but we never used that terminology when I was in school).

mathshelp · Apr 29, 2009, 07:49 AM

Originally Posted by Perito

1.
a. Multiply out the expressions, 7(6-3y) and 5(2y+4).
b. collect like terms (add/subtract constants, add coefficients of y
c. Subtract the constant from both sides.
c. Solve the equation for y by dividing by the coefficient of y.

2.
a. multiply both sides of the equation by 6 (to get rid of the denominators).
b. Add a constant (36) to both sides of the equation.
c. Divide both sides of the equation by the coefficient of y. That will solve for y in terms of x
(I think that's what it means to make "y" the subject, but we never used that terminology when I was in school).

Thanks for your help.
I have worked them out, please could you confirm if there right:

1.
42 - 21y + 10y + 20 = 4x + 9
42 + 20 - 21y + 10y
62 - 11y = 4x + 9
-11y = 4x + 9 - 62 (x -1)
11y = -4x + 53

y= 4x+53 /11

2.
24x/18 + 6 = 18y/12 - 36
24x/18 + 42 = 18y/12
24x + 42 = y/12
y/12 = 24x + 42
y = 24x+42/12

Perito · Apr 29, 2009, 08:00 AM

Originally Posted by mathshelp

Thanks for your help.

1.
42 - 21y + 10y + 20 = 4x + 9
42 + 20 - 21y + 10y
62 - 11y = 4x + 9
-11y = 4x + 9 - 62 (x -1) <-- not sure where that came from but you didn't carry it through so it's ok.
11y = -4x + 53

y= 4x+53 /11

1 is OK. 2 needs some work.

$\frac {4x}{3} +1 =\frac {3y}{2} - 6$

multiply by 6

$6 ( \frac {4x}{3} +1) =6 (\frac {3y}{2} - 6)$

$\frac {24x}{3} +6 =\frac {18y}{2} - 36$

$8x +6 =9y - 36$

You can take it from there.

mathshelp · Apr 29, 2009, 08:11 AM

Originally Posted by perito

1 is ok. 2 needs some work.

$\frac {4x}{3} +1 =\frac {3y}{2} - 6$

multiply by 6

$6 ( \frac {4x}{3} +1) =6 (\frac {3y}{2} - 6)$

$\frac {24x}{3} +6 =\frac {18y}{2} - 36$

$8x +6 =9y - 36$

you can take it from there.

thank you

this has helped me a lot.