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How To Solve Quadratic Equation?

Padmini Roy
15/06/2017 0 0

A. When a = 1 - Solving quadratic equations types x² + bx + c = 0.

  • Solving this type of quadratic equations results in solving a popular puzzle: finding two numbers knowing their sum and their product. Solving becomes simple and doesn't need factoring.
  • Example 1. Solve: x² - 26x - 72 = 0.
  • Solution. Both real roots have opposite signs. Write down the factor-pairs of c = -72. They are:
  • (-1 , 72)(-2 , 36)(-3 , 24)...Stop!The sum of the 2 real roots in this set is 21 = -b. The 2 real roots are -3 and 24.
  • Example 2. Solve: -x² - 26x + 56 = 0.
  • Solution. Roots have opposite signs. Write down factor-pairs of c = 56:
  • (-1, 56) (-2, 28)...Stop. This sum is 26 = b. According to the Diagonal Sum Rule, when a is negative, the answers are -2 and 28.
  • Example 3. Solve x² + 27x + 50 = 0.
  • Solution. Both real roots are negative. Write factor-sets of c = 50:
  • (-1, -50) (-2, -25)..Stop. This sum is -27 = -b. The 2 real roots are -2 and -25.
  • Example 4. Solve: x² - 39x + 108 = 0.
  • Solution. Both real roots are positive. Write the factor-sets of c = 108:
  • (1, 108) (2, 54) (3, 36)...Stop. This sum is 39 = -b. The 2 real roots are 3 and 36.
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