Expert: Lynn Houston - 9/15/2008

Question
QUESTION: I get so confused about these problems: what formula would i use?

Given the following equation: 2x+3y=4, answer if x decreases in value by two units , what is the corresponding change in y?

ANSWER: The easiest way to solve this is to make a table with x and y values.  Start with x = 0 and solve for y.  So (0,4), then do the same for x=2, 4,6,and 8.  So you're going to have

X    Y
6,  -8/3
4,  -4/3
2,   0
0,   4/3
-2,  8/3

Then, you can clearly see that for each 2 unit decrease of x, Y INCREASES by 4/3.

---------- FOLLOW-UP ----------

QUESTION: still sorta confused. is there a formula i could use instead like y-y1=x-x1 or is this the only way to do this problem?

Answer
There's no formula, it's more of a visual in this case.  The thing about math is that there are usually a lot of different ways to come up with the same answer.  And, unless your teacher, homework or test asks you to solve something a particular way, you should do it the way that makes the most sense to you.