Question

One root of $x^2 + kx - 8 = 0$ is square of the other. Then the value of $k$ is

• A. 2
• B. 8
• C. -8
• D. -2

Hint:

Always use Vieta's formulas: sum of roots = $-\frac{b}{a}$, product = $\frac{c}{a}$, and substitute given relationships.

Answer 1

The Correct Option is A

Let roots be $m$ and $m^2$. Sum of roots: $m + m^2 = -k$. Product of roots: $m^3 = -8$. From $m^3 = -8$, $m = -2$. Sum of roots = $-2 + 4 = 2$. So $-k = 2 \Rightarrow k = -2$. Checking the options — correct $k$ is $-2$, so the correct choice should be (d). % Quick tip