You are Here: Home >< Maths

# Function question! watch

1. Hi, I was just wondering what I was doing wrong on this C3 question It's probably something quite simple aswell

,
,

(a) Express gf in terms of and state its domain and range.

I ended up getting: With a range of:

Thanks,
Gra.
2. i reckon your gf in terms of x is fine, but then i would find the minimum, when the differential = 0 , i.e. when 8x+8=0, i.e. when x=-1, so gf(x)>= -1

might be wrong though!
3. I agree with your gf(x).

-5 is the y intercept, but not the minimum point.

Try completing the square.
4. (Original post by AnonyMatt)

-5 is the y intercept, but not the minimum point.

Try completing the square.
Oh of course! Duh. Silly me. It was a mental lapse, obviously.

Thankyou
5. I now still can't do the last part, part c!

Using these again:
,
,

(c) The equation gf(x) - 2f(x) = a where a is a constant, has no real roots. Show that a <-10

Thanks again,
Gra.
6. (Original post by born_to_be_different)
I now still can't do the last part, part c!

Using these again:
,
,

(c) The equation gf(x) - 2f(x) = a where a is a constant, has no real roots. Show that a <-10

Thanks again,
Gra.
4x^2 + 8x - 5 - 4x - 4 = a
4x^2 - 4x - (9+a) = 0

What's the condition for a quadratic to have no real roots?

### Related university courses

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: January 31, 2010
Today on TSR

### He lied about his age

Thought he was 19... really he's 14

### University open days

Wed, 25 Jul '18
2. University of Buckingham
Wed, 25 Jul '18
3. Bournemouth University
Wed, 1 Aug '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

## Groups associated with this forum:

View associated groups

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