1959 AMC 12 Problem 27

Attempt Problem 27 of the 1959 AMC 12 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1959 AMC 12 solutions, or check the answer key.

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27.

Which one of the following statements is not true for the equation

ix2x+2i=0, ix^2-x+2i=0,

where i=1?i=\sqrt{-1}?

The sum of the roots is 22

The discriminant is 99

The roots are imaginary

The roots can be found by using the quadratic formula

The roots can be found by factoring, using imaginary numbers

Answer: A
Concepts:complex numberquadraticVieta’s Formulas
Difficulty rating: 1360
Small Hint:

Use Vieta’s formula for the sum of the roots before solving the equation

Big Hint:

The sum is the negative of the xx-coefficient divided by the x2x^2-coefficient

Solution:

By Vieta’s formula, the sum of the roots is 1i=1i=i, -\frac{-1}{i}=\frac1i=-i, not 2.2. Also the discriminant is (1)24(i)(2i)=18i2=9. (-1)^2-4(i)(2i)=1-8i^2=9. The quadratic formula gives the imaginary roots ii and 2i,-2i, so the remaining statements are true.

Thus, the correct answer is A.

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