Turn on thread page Beta
 You are Here: Home

# p1 algebra watch

1. I just need to check something; when you multiply out (2√x + 3)² do you get 4x + 4√x + 9 ?

I also am a bit comfused at this question:

Solve the equation 4x² + 12x=0

f(x)=4x² + 12x + c
where c is a constant

b) Given that f(x) = 0 has equal roots, find the value of c and hence solve f(x)=0

2. No, you get 4x + 12√x + 9

4x² + 12x=0
x(4x+12)=0
x=0,-3

b^2-4ac = 0
4ac = b^2
c = b^2/4a

f(x)=4x² + 12x + 12^2/4*4
=4x^2 + 12x + 9
3. a) Factorise! 4x(x+3) = 0 - Can you see what to do from there?

b) if there are two equal roots the equation can be written as (2x - a)^2 = 0. Multiply this out and equate coefficients to get the value of a and hence c
4. (Original post by mik1a)
No, you get 4x + 12√x + 9
No, you get 4x + 6√x + 9.

Ben

EDIT [Oh, I see - I thought he was just stipulating a square root with the 2, sorry]
5. (2√x + 3)² = 4x + 12√x + 9

4x² + 12x=0
4x(x+3) =0
x= 0,-3

4x² + 12x + c =0
(2x + 3)(2x + 3) = 0
c=9
6. (Original post by Ben.S.)
No, you get 4x + 6√x + 9.

Ben
No, you get 4x + 12√x + 9
7. (Original post by Zapsta)
No, you get 4x + 12√x + 9
Not if you read it as it's written!

Ben
8. Firstly, (2sqrt(x) + 3)^2 = 4x + 12sqrt(x) + 9.

To solve 4x^2 + 12x=0 factorise out 4x to give 4x(x+3)=0 so the solutions are x=0 or -3.

If f(x) has equal roots, the discriminant is equal to zero. That is, b^2-4ac=0. We have a=4, b=12 and we want to find c. Therefore, 144 - 4(4)c=0 => c=144/16 = 9. Thus, f(x) = 4x^2 + 12x + 9 = (2x+3)^2 so the root is -3/2.

I hope this helps.
9. (Original post by Ben.S.)
Not if you read it as it's written!

Ben
Ah yeah, sorry the fonts on my computer change when I use symbols from the character map. I actually meant to write 4x + 12√x + 9 I can't think why I wrote 4x + 4√x + 9 instead.

Thanks everyone.
10. Hehe I beat you all to it

Turn on thread page Beta
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 26, 2004
Today on TSR

### Are you living on a tight budget at uni?

From budgets to cutbacks...

### University open days

1. University of Edinburgh
Sat, 22 Sep '18
2. University of Exeter
Undergraduate Open Days - Penryn Campus Undergraduate
Sat, 22 Sep '18
3. Loughborough University
General Open Day Undergraduate
Sat, 22 Sep '18
Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE