WAEC 2020 · Paper 1 · Q38

Polynomials & quadratic roots

If the sum of the roots of $2x^2 + 5mx + n = 0$ is 5, find the value of $m$ .

Worked solution (try it first)

For $ax^2 + bx + c = 0$ , the sum of the roots is $-\dfrac{b}{a}$ .
Here that is $-\dfrac{5m}{2}$ .
Set $-\dfrac{5m}{2} = 5$ , so $-5m = 10$ .
So $m = -2$ , option B.

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