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# Maths C1 Inequalities Question watch

1. Find the set of of values for which x* - 4x - 5 > 0 (* means 'squared')

(x+1)(x-5)=0

x=-1 or x=5

The required set of values is x<-1 or x>5

I don't understand this, if x* - 4x - 5 > 0 then why are the values of x less than -1 and more than 5? Being less than -1, means its less than 0 so...
2. It means there are two possible regions of x that satisfy the inequality. They don't occur at the same time.
3. When you think of the graph of you are really drawing x against y. It is asking what are the values of x when y > 0 (or above the x axis). It is clear that x has to be less than -1 or more than 5 for y being more than 0.
4. the values of the function of x are more than zero.
This is the case when the x values are less than -1, and more than 5.
sub the values into the function and it will make sense.
5. (Original post by soup)
When you think of the graph of you are really drawing x against y. It is asking what are the values of x when y > 0 (or above the x axis). It is clear that x has to be less than -1 or more than 5 for y being more than 0.
When y>0, x could also be 2, 3 ,4 or -0.5?
6. (Original post by xXxiKillxXx)
When y>0, x could also be 2, 3 ,4 or -0.5?
No when y>0 x has to be less than -1 or more than 5. Look at the graph!
7. (Original post by xXxiKillxXx)
When y>0, x could also be 2, 3 ,4 or -0.5?
No, if you look at the graph, the bit that is below the x-axis has values of y < 0, so they don't satisfy the equation, as its asking for values greater than 0. So you look at the lines above the x-axis, where all values of y > 0, and this is where you get x<-1, and x>5, because those x-values satisfy the values of y > 0. I hope I made sense.. :P
8. (Original post by xXxiKillxXx)
When y>0, x could also be 2, 3 ,4 or -0.5?
no, it couldn't. because y is given in terms of x.
let me give an example

in this case
because
and
but, so you can see if x doesn't satisfy
does not satisfy the inequality.
9. When you factorise it, imagine sketching the graph out. So you know that it's a quadratic and it crosses the x axis at -1 and 5 . After sketching the graph, see what parts of the graph is greater than 0 . These should be the range that they're asking for, so those are the ranges that its greater than zero, which is x <-1 or x >5
10. Dont get it :/
11. (Original post by xXxiKillxXx)
Dont get it :/
For what values of x is the curve above the x axis?
12. (Original post by xXxiKillxXx)
Dont get it :/
I attached a picture to try and make things clearer. The blue line represents all values of the equation: x^2 - 4x - 5 which are greater than 0. The red line represents all values of the equation: x^2 - 4x - 5 which are less than 0. As the questions is asking what values of the equation: x^2 - 4x - 5 are greater than 0, only values on the blue line satisfy this. The only was this is possible is if x < -1, and x > 5.

If you're still unsure:
You've got the equation x^2 - 4x - 5.
Put in x = -2. You get (-2)^2 - 4(-2) - 5 = 7
Put in x = -0.5. You get (-0.5)^2 - 4(-0.5) - 5 = -3.25

Put in x = 4. (4)^2 - 4(4) - 5 = -5
Put in x = 6. (6)^2 - 4(6) - 5 = 7

Any value less than -1, or greater than 5 will result in a positive value, i.e. one that is greater than 0. You only get negative values if you try any value between -1 and 5.

Edit: Graph sourced from http://www.wolframalpha.com
Attached Images

13. (Original post by xXxiKillxXx)
Dont get it :/
I saw your other thread asking for the marks you should be getting in C1 for Cambridge. TBH, you don't have a chance if you're struggling with such a simple concept at this stage
14. (Original post by soup)
No when y>0 x has to be less than -1 or more than 5. Look at the graph!

OP LOOK AT THE GRAPH
15. (Original post by xXxiKillxXx)
When y>0, x could also be 2, 3 ,4 or -0.5?

No. Try subsituting those values into the equation you find that y<0 and not y>0 that's understandably, because the graph proves it!
16. (Original post by BieberFan)
I saw your other thread asking for the marks you should be getting in C1 for Cambridge. TBH, you don't have a chance if you're struggling with such a simple concept at this stage
I'm a motivated man, we will see in March or whenever the C1 results come out
17. (Original post by xXxiKillxXx)
I'm a motivated man, we will see in March or whenever the C1 results come out
It's not about being motivated. It's about talent. You'll be proved to be a 'try-hard', who lacks ability, if you get to interview, in which case, you won't get an offer.
18. oh please, we are dealing with f(x) here, not x, y= f(x) ehh so you can scetch the graph and find where f(x) ie y is more than 0
19. (Original post by BieberFan)
It's not about being motivated. It's about talent. You'll be proved to be a 'try-hard', who lacks ability, if you get to interview, in which case, you won't get an offer.
Haha haters dont phase me, i aint realistic in life as i believe i can achieve anything

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