Of course, both of the numbers can be zero since (0)(0) = 0. We can never multiply two numbers and obtain an answer of zero unless at least one of the numbers is zero. We will not attempt to prove this theorem but note carefully what it states. In other words, if the product of two factors is zero, then at least one of the factors is zero. The method of solving by factoring is based on a simple theorem. This method cannot always be used, because not all polynomials are factorable, but it is used whenever factoring is possible. The simplest method of solving quadratics is by factoring. It is possible that the two solutions are equal.Ī quadratic equation will have two solutions because it is of degree two. This theorem is proved in most college algebra books.Īn important theorem, which cannot be proved at the level of this text, states "Every polynomial equation of degree n has exactly n roots." Using this fact tells us that quadratic equations will always have two solutions. The solution to an equation is sometimes referred to as the root of the equation. In other words, the standard form represents all quadratic equations. The standard form of a quadratic equation is ax 2 + bx + c = 0 when a ≠ 0 and a, b, and c are real numbers.Īll quadratic equations can be put in standard form, and any equation that can be put in standard form is a quadratic equation. Solve a quadratic equation by factoring.Ī quadratic equation is a polynomial equation that contains the second degree, but no higher degree, of the variable.Place a quadratic equation in standard form.Upon completing this section you should be able to: QUADRATICS SOLVED BY FACTORING OBJECTIVES You now have the necessary skills to solve equations of the second degree, which are known as quadratic equations. In previous chapters we have solved equations of the first degree. All skills learned lead eventually to the ability to solve equations and simplify the solutions. So this checks out.Solving equations is the central theme of algebra. Which is negative 9, plus 9, does indeed equal 0. Negative 7 times 1, right? That's negative 1 squared. Squared- negative 1 squared is just 1- so this would be Verify for yourself that they satisfy it. Substitute these q's back into this original equation, and So q could be equal to negativeġ, or it could be equal to 9 over 7. Negative 18 divided by negative 14 is equal Negative 2 plus 16 is 14 dividedīy negative 14 is negative 1. Minus, that plus is that plus right there. Or negative 2 minus- right? This is plus 16 over Thing as being equal to negative 2 plus 16 And what's 256? What's the square root of 256? It's 16. Negative 2 plus or minus the square root of- what'sĤ plus 252? It's just 256. Now what does this equal? Well, we have this is equal to And then our denominator,Ģ times negative 7 is negative 14. We have a positive 252 for that part right there. Negative 7 and you have a minus out front. So it's just going to becomeĪ positive number. Here, if we just take the negative 4 times negativeħ times 9, this negative and that negative is going To negative 2 plus or minus the square root of- let's see,Ģ squared is 4- and then if we just take this part right All of that over 2 timesĪ, which is once again negative 7. Of b squared, of 2 squared, minus 4 times a times negativeħ times c, which is 9. Us that the solutions- the q's that satisfy thisĮquation- q will be equal to negative b. And if we look at it, negativeħ corresponds to a. So if we look at the quadraticĮquation that we need to solve here, we can just Take the positive square root and there's another solution Solutions here, because there's one solution where you Square root of b squared minus 4ac- all of that over 2a. X is going to be equal to negative b plus or minus the That the solutions of this equation are going to be Look, if you have a quadratic equation of this form, We could put the 0 on the left hand side. Now, the quadratic formula, itĪpplies to any quadratic equation of the form. Solve the equation, 0 is equal to negative 7q squared So you can see we have to use plus or minus, because when you solve a quadratic equation, very often there are two solutions, those being some value, lets call it 'a', and its negative, that is '-a'. We can write these two solutions as x=☒, which means x=2 and x=-2. So this quadratic equation has TWO solutions. I am sure you know that 3x3=9, so x=3 is a solution, right?īut what about -3? (-3)(-3) also equals 9, (-3)(-3)=9, so x=-3 as well. Y=x² is a quadratic expression since it has a x² term and there is no other term with a greater exponent. What is that? It is an expression that has a variable raised to the power 2 AND that the power 2 is the largest power in the expression: eg x²+2x+1 is a quadratic expression, but 2x+1 is not (no x²), nor is x³+x²+2x+1 (the power 3 in x³ is too big.) We used the quadratic equation because we are solving a quadratic expression.
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