>How do you solve for x in the equation X*(X+20)=2400
>
>Thanks
>Jon
A quadradic equation can be solved by several methods. Many of these require you to first put the equation in the standard form, which in this case is X^2 + 20X - 2400 = 0:
Trial-and-error, which probably is the idea for the fourth grade.
Factoring, which also involves some trial-and-error.
Completing the square (complete a perfect square on the left side).
The quadratic formula. You can always use this one, or try other methods first and reserve the quadratic formula for the "tougher" cases.
Notice the "plus-or-minus" in the quadratic formula. Depending on the discriminant (the value under the square root (b squared - 4ac)), the quadratic equation will have 2 real solutions (if the discriminant is positive), 1 solution (if the discriminant is zero), or no real solution (but two complex solutions) if the discriminant is negative).
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
