standard form of an equation
An equation is in standard form if the only term on the right-hand side of the equation is zero.
For example, the equations 6x2 + 2x – 3 = 0 and x4 – 5 = 0 are both in standard form. The equation 6x2 + 2x = 3 and x4 = 5 are not in standard form.
Certain equations that are not quadratic can be expressed in quadratic form using substitutions. These equations can be recognized because when they are written in standard form, the exponent of the variable in one term is half the exponent of variable in the other term.
For example, we can write standard form equations such as x4 + 17x2 + 72 = 0
2x8 + 4x4 = 0 x – ñx – 12 = 0
as quadratic equations, because the exponent of the first variable is twice the exponent of the second variable.
Look at the steps to write an equation as a quadratic.
1.Let t be a variable term with the half exponent.
2.Substitute t in all the terms with the variable.
3.Solve for t.
4.Back substitute for the original variable.
Solve x4 – 13x2 + 36 = 0.
The equation x4 – 13x2 + 36 = 0 is not a quadratic equation but we can write it as (x2)2 – 13x2 + 36 = 0. For this reason, it is a quadratic in x2. Let x2 = t.
First we solve for t, then solve the resulting equations for x. (x2)2 – 13x2 + 36 = 0
x2 = t, so t2 – 13t + 36 = 0. By factoring, (t – 4)(t – 9) = 0
t = 4 or t = 9. Since t = x2
x2 = 4 |
|
x2 = 9 |
x = 2 |
or |
x = 3 . |