Equations with an order of 2 (contains a value to the power of 2, i.e. x2).
An example of a quadratic equation is:
x2 + 10x + 7
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If you're talking about two linear equations, make sure they are not parallel. If you're talking about quadratics, make sure that b2-4ac is not negative.
Many real life physics problems are parabolic in nature. Parabolas can be shown as a quadratic equation. If you have two variables then usually you can use the equation to find the best solution to a problem. Also, it is a beginning in the world of mathematical optimization. Some equations use more than two variables and require the technique used to solve quadratics to solve them. I just ran an optimization of 128 variables. To understand the parameters I needed to set I had to understand quadratics.
X^2 - 2X - 48 = 0 what two factors of - 48 add up to - 2 ? (X + 6)(X - 8) X = - 6 --------- X = 8 ---------by inspection can solve many quadratics
The simplest example that fits that is y = x^2 - 7x + 12. A math professor wouldn't like the process, but assuming we want a positive quadratic, and since positive quadratics are symmetrical along their minimums, we can skip some steps. We know that the local minimum is going to lie exactly between 3 and 4, at x = 7/2. Put everything on one side to get 2x - 7 = 0. Taking the integral (and skipping a few more steps) gets y = x^2 - 7x + c. Solving for c where y = 0 when x = 3, we find c = 12.
One pro of using the quadratic formula is that it will produce complex (imaginary) roots just as easily as it can produce real roots. (Factoring with imaginary numbers is a kind of a nightmare!) Another pro to the quadratic formula is that it eliminates the frustrating guess-and-check process. A con of the quadratic formula is that, when it comes to more simple problems, it is usually more time-consuming. A lot of textbook problems are quite easy to factor in your head--it is often not worth the effort of plugging numbers into a long formula. A second con of the quadratic formula is that it is quite long--you might write out the formula, accidentally forget a letter, and whole thing is useless. It's much easier to see that your work is correct when you're factoring.