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Linear and Quadratic Equations · Question 63 of 66

Question 63

MediumOriginal question

If α\alpha and β\beta are the roots of x2−7x+10=0x^2 - 7x + 10 = 0, what is α2+β2\alpha^2 + \beta^2?

Options for question 63

Show the answer and explanation
CorrectNot quiteAnswer A

Correct answer: A

Explanation

  1. α+β=7\alpha + \beta = 7 and αβ=10\alpha\beta = 10.

  2. α2+β2=(α+β)2−2αβ=49−20=29\alpha^2 + \beta^2 = (\alpha + \beta)^2 - 2\alpha\beta = 49 - 20 = 29.

  3. Check with the roots 2 and 5: 4+25=294 + 25 = 29.

Worth noting

49 is (α+β)2(\alpha + \beta)^2 alone; 39 subtracts αβ\alpha\beta once instead of twice; 69 adds 2αβ2\alpha\beta instead of subtracting it.

Concept
Symmetric expressions of roots from sum and product
Typical time
70 s
Your time
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The rule this testsRoots and their nature
Practise this chapter →

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

Practise this chapter →

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