Hi all, this is my first post

Having issues with this question: “In the xy-plane, the graph of equation y = -1/2x + 3 passes through (c, -c). What is the value of c?”

I pretty much just plugged in (c, -c) into the equation and came out with 6. Problem is, the answer is -6…

Here was my logic…

-c = -1/2c + 3 <— divide -c by -1/2c

= 1/2c = 3 <— multiply 3*2 to get 6 on right side of equation

Answer = c = 6. **But it’s wrong!**

Any idea how to get -6 (the right answer?). Thanks!!

Here’s a GMAT club explanation but I still don’t get it: In the xy-plane, the graph of the equation y = -1/2*x+3 passes through : Problem Solving (PS)

Hello @gillenheisler1! I think you might be making an error while solving the equation you set up. This is because when you are dividing by -1/2 you are making an error. -c/(-1/2) would equal 2c (An easy way to check this is to substitute 2 as c and divide it by 0.5 in your calculator and you’ll notice the answer is 4).

You also made a division error on the right. You have to divide every term in the equation on both sides by -1/2 if that’s your intent. This is how it would play out:

-c = -1/2c + 3

-c/(-1/2) = -1/2*c/(-1/2) + 3/(-1/2)

2c = c - 6

2c - c = -6

c = -6

I found it easier to set it up this way:

-c = -1/2c + 3

-c - 3 = -1/2 c (I took the 3 on the RHS and move it to the LHS so signs change)

2(-c - 3) = -c (I took the 2 and I moved it to the LHS so now we multiply it)

-2c - 6 = -c (multiplying with the 2)

-2c + c = 6 (moved the c to the LHS and 6 to the RHS so signs change)

-c = 6 or c = -6

Hope this helps!