10 Quadratic Equations
10.3 Solving Quadratic Equations by the Quadratic Formula Objectives 1. Identify the values of a, b, and c in a quadratic equation. 2. Use the quadratic formula to solve quadratic equations. 3. Solve quadratic equations with only one solution. 4. Solve quadratic equations with fractions.
Note In ax2+bx+c=0, there is a restriction that a is not zero. If it were, the equation would be linear, not quadratic.
Identify the Values of a, b, and c in Quadratic Equations Example 1 Identify the values of the variables of a, b, and c, in each quadratic equation ax2 + bx + c = 0. (a) –3x2 + 5 = 2x Write the equation in standard form ax2 + bx + c=0. –3x2 –2x + 5 = 0 a = –3, b = –2, and c = 5
Identify the Values of a, b, and c in Quadratic Equations Example 1 (continued) Identify the values of the variables of a, b, and c, in each quadratic equation ax2 + bx + c = 0. (b) (x – 2)(x + 2) = 0 x2 – 4 = 0 Multiply using the FOIL method. x2 + 0x – 4 = 0 The x-term is missing, so write the equation with 0 as the coefficient of the x-term. a = 1, b = 0, and c = –4
Use the Quadratic Formula to Solve Quadratic Equations Step 1 Transform so that the coefficient of x2 is equal to 1. Standard form Divide by a. Step 2 Write so that the variable terms with x are alone on the left side. Subtract .
Use the Quadratic Formula to Solve Quadratic Equations Step 3 Add the square of half the coefficient of x to each side, factor the left side, and combine terms on the right. Add . Factor; add on right.
Use the Quadratic Formula to Solve Quadratic Equations Step 4 Use the square root property to complete the solution.
Use the Quadratic Formula to Solve Quadratic Equations The solutions of the quadratic equation ax2 + bx + c, a ≠ 0, are or in compact form,
Use the Quadratic Formula to Solve Quadratic Equations CAUTION Notice in the quadratic formula that the fraction bar is under –b as well as the radical. Be sure to find the values of first, and then divide those results by the value of 2a.
Use the Quadratic Formula to Solve Quadratic Equations Example 2 Solve 3x2 + 4x – 5 = 0. In this equation, a = 3, b = 4, and c = –5.
Solve Quadratic Equations with Only One Solution Example 4 Solve 16x2 – 24x + 9 = 0. In this equation, a = 16, b = –24, and c = 9. There is just one solution in the solution set,
Solve Quadratic Equations with Fractions Example 5 Solve . Standard form Clear fractions; multiply by the LCD, 4. 4x2 – 26x + 46 = 0 Multiply. In this equation, a = 4, b = –26 , and c = 46.
Solve Quadratic Equations with Fractions Example 5 (concluded) Solve . is not a real number. The solution set is