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Linear and Quadratic Equations · Question 64 of 66

Question 64

HardOriginal question

If α\alpha and β\beta are the roots of 2x2−6x+3=02x^2 - 6x + 3 = 0, what is αβ+βα\frac{\alpha}{\beta} + \frac{\beta}{\alpha}?

Options for question 64

Show the answer and explanation
CorrectNot quiteAnswer B

Correct answer: B

Explanation

  1. α+β=62=3\alpha + \beta = \frac{6}{2} = 3 and αβ=32\alpha\beta = \frac{3}{2}.

  2. αβ+βα=α2+β2αβ\frac{\alpha}{\beta} + \frac{\beta}{\alpha} = \frac{\alpha^2 + \beta^2}{\alpha\beta}.

  3. α2+β2=9−2×32=6\alpha^2 + \beta^2 = 9 - 2 \times \frac{3}{2} = 6.

  4. So the value is 63/2=4\frac{6}{3/2} = 4.

Worth noting

6 is α2+β2\alpha^2 + \beta^2 before dividing by αβ\alpha\beta. Taking the product as 3 (forgetting to divide by a=2a = 2) gives 9−63=1\frac{9 - 6}{3} = 1. Using α2+β2=9−32\alpha^2 + \beta^2 = 9 - \frac{3}{2} gives 5.

Concept
Expressions in the roots via sum and product
Typical time
120 s
Your time
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The rule this testsRoots and their nature
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Ten questions from Linear and Quadratic Equations, at your own pace.

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Ten questions from Linear and Quadratic Equations, at your own pace.