Expert: Scott A Wilson - 2/5/2011

Question
ax+b=0 for x

Answer
Looking at ax + b = 0, we want to solve for x.
The 1st thing to do is get the x term by itself.
The b term has no x, so subtract b from both sides.
This gives ax + b - b = 0 - b which turns into ax = -b.

Now that the x term is isolated, divide by the multiplier in front, which is a.
That gives ax/a = -b/a, and ax/a is just x, so the equation is x = -b/a.

The last step, which is frequently forgotten, is to put that back in the starting equation.
That is, put x = -b/a into ax + b = 0 and get a(-b/a) + b = 0.
Now the first term is multiplied together, so we get -ab/a + b = 0.

Since -ab/a has the a's in the top and bottom cancel, the 1st term is just -b.
Putting that back in, we get -b + b = 0, and the is correct, so the the problem is also correct.