# Thread: Quadratic Formula - Help needed

1. ## Quadratic Formula - Help needed

HI

How is this solved with quadratic formula:

3n^2-21n+38=20

ps. I put 3 instead of a, 21 instead of b, and 38 instead of c, but I can't get the result I want.
I know n=6, but how do i get this..?

2. Originally Posted by alternative
HI

How is this solved with quadratic formula:

3n^2-21n+38=20

ps. I put 3 instead of a, 21 instead of b, and 38 instead of c, but I can't get the result I want.
I know n=6, but how do i get this..?
$b = -21$

$c = 18$

3. could I ask why c=18, thanks a lot

4. Originally Posted by alternative
could I ask why c=18, thanks a lot
because the quadratic equation works if $ax^2 + bx + c = 0$

5. ouppppssss :\$

Thank you, so so so much..