Multiple choice

If one root of the equation $ ax^{2}+bx+c=0 $ is $3-4i$, then $a+b+c$ is equal to

  1. $40$
  2. $36$
  3. $-20$
  4. $20$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Since coefficients are real, if 3-4i is a root, then 3+4i is also a root. Sum of roots = 6 = -b/a. Product of roots = 3^2 + 4^2 = 25 = c/a. Equation is x^2 - 6x + 25 = 0. a=1, b=-6, c=25. a+b+c = 1 - 6 + 25 = 20.

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