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Week 7 – Interpreting The Discriminant

The expression, b2  – 4ac, is called the discriminant of the quadratic equation. The discriminant tells us how many solutions an equation has.

The quadratic equation ax2 + bx + c = 0 has:

  • two real roots when  b2  – 4ac > 0

ex. x2 – 6x + 5 = 0

(-6) – 4(1)(5)

36 – 20

= 16

 

  • one real root when b2  – 4ac = 0

ex. x2 – 6x + 9 = 0

(-6)2 – 4(1)(9)

36 – 36

= 0

  • no real roots when b2  – 4ac < 0

ex. x2 – 6x + 13 = 0

(-6)2 – 4(1)(13)

36 – 52

= -16

sarahl22015 • April 8, 2018


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