# Math Help - inequality discriminants

1. ## inequality discriminants

hi all, the question is: obtain an inequality satisified by k if the equation below has two distinct real roots

$x^2 - 2x - k = 0$

so i made that into $4 - 4k > 0$ then

$-4k > -4$ then i would presume the final answer is

$k > 1$

but the books answer is k > -1

why is this? thanks

Mark

2. Originally Posted by mark
hi all, the question is: obtain an inequality satisified by k if the equation below has two distinct real roots

$x^2 - 2x - k = 0$

so i made that into $4 - 4k > 0$ then

$-4k > -4$ then i would presume the final answer is

$k > 1$

but the books answer is k > -1

why is this? thanks

Mark
You need to add 4k because -4ac = -4*1*-k = +4k

From there solve to give the book's answer

3. ha woops, yeah that was a stupid mistake. thanks though