Definition In mathematics, a quadratic equation is a polynomial equation of the second degree. The general form is where x represents a variable or an unknown, and a, b, and c are constants with a # 0. (If a = 0, the equation is a linear equation.) The constants a, b, and c are called respectively, the quadratic coefficient, the linear coefficient and the constant term or free term.
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Quadratic & Roots Quadratic: A polynomial of degree-2 O is a quadratic equation. (a # 0 ) Here is an example of one: this makes it Quadratic The name Quadratic comes from "quad" meaning square, because the variable gets squared (like It is also called an "Equation of Degree 2" (because of the "2" on the x)
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Roots A real number a is called a root of the 2 quadratic equation ax if aa2 + ba2 + c = 0. 2 If a is a root of ax say that: = 0 ,then we (i) a satisfies the equation ax2+bx+c Or (ii) a is a solution of the equation aX2-l-bX+C The Root of a quadratic equation ax2+bx+c zeros of the polynomial are called
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More Examples of Quadratic Equations 2 + 51' +3—0 In this one a=2, and c=3. 2 3r = 0 This one is a little more tricky: Where is a? In fact a-I , as we don't usually write "1 b = -3 and where is c? Well, c=O, so is not shown. 51 —3=0 Oops! This one is not a quadratic equation, because it is missing (in other words a=O, and that means it can't be quadratic)
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Hidden Quadratic Equations! So far we have seen the "Standard Form" of a Quadratic Equation: 2 ax But sometimes a quadratic equation doesn't look like that..! Here are some examples of different form: In disguise = 3x -1 2(w2 - 2w) = 5 z(z-l) = 3 1/x2 = Move al/ terms to left hand side Expand (undo the brackets), and move 5 to left Expand, and move 3 to left Multiply by x2 In Standard Form - 3x +1 = O 2w2 - 4W - 5 = O z2 -z -3=0 5x2 + x -1 = O a, b and c a-I, b=-3, a-I, b=-l, c=-3 a=5, , c=-l
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How To Solve It? There are 3 ways to find the solutions: + We can Factor the Quadratic (find what to multiply to make the Quadratic Equation) + We can Complete the Square, or + We can use the special Quadratic Formula: - b2-4ac Thus ax2+bx+c has two roots a and ß, given by —b— b2—4ac 2a
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Discriminant The expression in the formula It is called the Discriminant, because it can "discriminate" between the possible types of answer.lt can be denoted by "D" when b2 - 4ac, D is positive, you get two real solutions you get just ONE real solution (both answers are when it is zero the same) when it is negative you get two Complex solutions Value of D Nature of Roots Real and Unequal Real and Equal No real roots Roots Each root = (-b/2a) None
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Using the Quadratic Formula Just put the values of a, b and c into the Quadratic Formula, and do the calculation Solve + + 1 = o Example: Coefficients are Quadratic Formula: x = Put in a, b and c: [ -b ± N(b2-4ac) ] / 2a 62 -4x5x1 (2x5) 20 Solve: 6 + 36 (10) 6 ± (16) (10) (10) = -0.2 or -1
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Continue, , Answer: x = -0.2 or x = -1 + Check -0.2: + 6x(-o.2) + 1 = -1.2+1 + Check -1: + + 1 = 5-6+1
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Factoring Quadratics + To "Factor" (or "Factorize") a Quadratic is to find what to multiply to get the Quadratic It is called "Factoring" because you find the factors (a factor is something you multiply by) Example The factors of + 3x - 4 are: and Why? Well, let us multiply them to see: Multiplying together is called Expanding. In fact, Expanding and Factoring are opposites: Expand x2+ 3x 4 Factor
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Examples of Factor To solve by factoring: 1. Set the equation equal to zero. 2. Factor. The factors will be linear expressions. 3. Set each linear factor equal to zero. 4. Solve both linear equations. Example: Solve by factoring set equation to zero factor x = -3 set the linear factors equal to zero and solve the linear equation
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Completing the Square Solving General Quadratic Equations by Completing the Square: "Completing the Square" is where we take a Quadratic Equation : ax2 + bx + c = 0 and turn into We can use that idea to solve a Quadratic Equation (find where it is equal to zero). But a general Quadratic Equation can have a coefficient of a in front of But that is easy to deal with ... just divide the whole equation by " first, then carry on.
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Steps Now we can solve Quadratic Equations in 5 steps: Step 1 Divide all terms by a (the coefficient of Step 2 Move the number term (c/a) to the right side of the equation. Step 3 Complete the square on the left side of the equation and balance this by adding the same value to the right side of the equation. Step 4 Take the square root on both sides of the equation. Step 5 Add or subtract the number that remains on the left side of the equation to find x.
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Example Example 1: Solve + 4x + 1 = O Step 1 can be skipped in this example since the coefficient of is 1 Step 2 Move the number term to the right side of the equation: Step 3 Complete the square on the left side of the equation and balance this by adding the same number to the right side of the equation: Step 4 Take the square root on both sides of the equation: x + 2 = = ±1.73 (to 2 decimals) Step 5 Subtract 2 from both sides: x = ±1.73-2 = -3.73 or -0.27
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