You may want to review the old ways of solving them first.

There is a general formula for solving *any* quadratic
equation. Suppose the equation looks like *ax*^{2}
+ *bx* + *c* = 0. (You can make any quadratic equation
look like that by getting everything on one side and collecting
like terms.) Then the solutions are (−*b* ±
√(*b*^{2} − 4*ac*)) / (2*a*).
The ± symbol means “plus or minus”; so there
are two solutions (unless the thing inside the square root is 0),
one with a + and one with a −.

It's strongly recommended that you memorize this formula. If you change it even a bit, you'll get completely wrong answers.

It's also recommended that, when you see a quadratic equation, you first consider for a second or two whether you can solve it by one of the earlier methods. Since they're much more intuitive, you're less likely to make careless errors with them.