quadratics help needed

14041471 · #1 $Old$ January 1st, 2009, 09:45 AM

I need to solve for x in these two question;
x: -3x2 + 4x = 4
x: x2 + 3x + 4 = 0

I'm quite sure there will be two awnsers for each question
I tried plugging in the numbers into this formula -b+/- sqrt> b^2 -4(a)(c)/2a
i need somebodies help because my arithmatic is bad, and i cant seem to get a whole number as my awnser so im stuck

janvdl · #2 $Old$ January 1st, 2009, 10:27 AM

Quote:

Originally Posted by 14041471 $View Post$

I need to solve for x in these two question;
x: -3x2 + 4x = 4
x: x2 + 3x + 4 = 0

I'm quite sure there will be two awnsers for each question
I tried plugging in the numbers into this formula -b+/- sqrt> b^2 -4(a)(c)/2a
i need somebodies help because my arithmatic is bad, and i cant seem to get a whole number as my awnser so im stuck

Correct, they are not whole numbers, and the roots are complex.

14041471 · #3 $Old$ January 1st, 2009, 11:31 AM

i no you've helped me out alot already, but i really cant awnser this question. could you solve it for me and then mabe i could see how it is like that..

janvdl · #4 $Old$ January 1st, 2009, 01:05 PM

Quote:

Originally Posted by 14041471 $View Post$

i no you've helped me out alot already, but i really cant awnser this question. could you solve it for me and then mabe i could see how it is like that..

You said you plugged it into the quadratic formula. That is all you need to do.

I will do the second one for you. The first one you must attempt on your own.

$x = \frac{ -b \pm \sqrt{b^2 - 4ac} }{2a}$

$x = \frac{ -3 \pm \sqrt{9 - 4(1)(4)} }{2(1)}$

$x = \frac{ -3 \pm \sqrt{7} }{2}$

$x = -1.5 + \frac{ \sqrt{-7} }{2}$
OR
$x = -1.5 - \frac{ \sqrt{-7} }{2}$

Thus:

$x = -1.5 + \frac{ \sqrt{7} }{2}i$
OR
$x = -1.5 - \frac{ \sqrt{7} }{2}i$

mr fantastic · #5 $Old$ January 1st, 2009, 01:45 PM

Quote:

Originally Posted by 14041471 $View Post$

i no you've helped me out alot already, but i really cant awnser this question. could you solve it for me and then mabe i could see how it is like that..

It would be easier to help you and point out your mistakes if you showed the work you've done.