# Solve for x

• Apr 13th 2008, 03:03 AM
delicate_tears
Solve for x- REALLY REALLY URGENT
y= 3(2x + 1)^2 - 5. Please show all working out >.<
• Apr 13th 2008, 03:05 AM
Moo
Hello,

Why don't you try a little on your own ?

And what exactly d'you want ? Solve for y=0 ? Or express x with y ?
• Apr 13th 2008, 03:22 AM
delicate_tears
Quote:

Originally Posted by Moo
Hello,

Why don't you try a little on your own ?

And what exactly d'you want ? Solve for y=0 ? Or express x with y ?

I wanted to solve for x, hence the topic. I tried it before , but I got (-1 + square root 15) /2, which was totally not the answer. That's why I wanted the steps, to show me how to get there. I know the answer, it's 0.145... and -1.145... I just need to know how to get round it.
• Apr 13th 2008, 03:26 AM
janvdl
Quote:

Originally Posted by delicate_tears
y= 3(2x + 1)^2 - 5. Please show all working out >.<

$\displaystyle y = 3(2x + 1)^2 - 5$

$\displaystyle y + 5 = 3(2x + 1)^2$

$\displaystyle \frac{y + 5}{3} = (2x + 1)^2$

$\displaystyle \sqrt{ \frac{y + 5}{3} } = 2x + 1$

$\displaystyle \sqrt{ \frac{y + 5}{3} } - 1 = 2x$

$\displaystyle \frac{ \sqrt{ \frac{y + 5}{3} } - 1 }{2} = x$
• Apr 13th 2008, 03:28 AM
Moo
You want to solve for x in 3(2x + 1)^2 - 5=0

This is completely different than your previous question ^^

Well

3(2x+1)²=5

(2x+1)²=5/3

2x+1=sqrt(5/3) or -sqrt(5/3) remember this ! (a)²=(-a)²=a² (Wink)

2x=-1+sqrt(5/3) or -1-sqrt(5/3)

And then divide by 2.
• Apr 13th 2008, 03:35 AM
Moo
Quote:

Originally Posted by janvdl

$\displaystyle \sqrt{ \frac{y + 5}{3} } = 2x + 1$

OR

$\displaystyle -\sqrt{ \frac{y + 5}{3} } = 2x + 1$

Don't forget it :p