Question

For what value of $a$, the curve $y=x^2+ax+25$ touches the $x$-axis

• A. $0$
• B. $\pm 5$
• C. $\pm 10$
• D. none

Answer 1

The correct option is C $\pm 10$

$y=x^2+ax+25$
Since the graph of the curve touches $x$-axis that means the curve has equal roots.
$D=0$
$a^2-100=0$
$a=\pm 10$.