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Algebra/How to rewrite an equation so that y is function of x

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Question
How do I rewrite this equation to solve for y
30=9x-5y

Answer
Hi Hunter, I'm glad to be of assistance.

In order to solve for y, you need to isolate the y term, meaning anything that is not y or a coefficient (the number directly in front of y) must be brought to the other side of the equation.  Here, in your example, we need to bring 9x to the other side.  Notice 9 is positive, so to move it, subtract 9x from both sides to get

30 - 9x = -5y (make sure you keep the negative, or -, in front of the y, that doesn't disappear and that is a mistake many make)

Or

-9x + 30 = -5y (your teacher may want the x term first)

Since y is being multiplied by negative five, to get rid of it, you must divide both sides by -5, since -5/-5 = 1.

When you do this, you get

(9/5)x - 6 = y (do you see the sign changes because of division by a negative?)

Or

y = (9/5)x - 6

Note: the coefficient of y is 1 but it is unnecessary to show this.

The equation is now solved for y.

I hope this helps.  

Algebra

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Anne Losch

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