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Quick question

F(X) = 10 - (x + 3 ) ^2

Is this correct

- (x + 3 ) ^2 + 20

Maximum point = x = -3 y =10 ?
Original post by IShouldBeRevising_


- (x + 3 ) ^2 + 20


Where does the 20 come from?
Is this June 05? XD
You're right. Another way to think about it is that it's a quadratic with translation 10 units up, therefore the max point will be y=10
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TenOfThem
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Original post by IShouldBeRevising_
F(X) = 10 - (x + 3 ) ^2

Is this correct

- (x + 3 ) ^2 + 20

Maximum point = x = -3 y =10 ?


No

Yes the maximum point is (-3, 10)
If that second expression is a derivative, then no. Use chain rule or expand brackets.

Edit: Aha, so it's a completing the square thing? Why do you have 10 and then 20?
(edited 10 years ago)
Original post by TenOfThem
No

Yes the maximum point is (-3, 10)



Original post by eggfriedrice
Is this June 05? XD
You're right. Another way to think about it is that it's a quadratic with translation 10 units up, therefore the max point will be y=10


Thats incorrect... Im not thinking of it like this you would be right if the equation was 10 -x^2... I think anyway lol

Original post by maggiehodgson
Where does the 20 come from?


Yeah sorry guys it was suppose to be a 10...

and yes this in june 05

btw can you anybody help with this question I have

| 6x - 1 | = | x - 1 |

Basically I squared both sides as squaring gets rid of both mod signs and solved the quadratic and obtained x = 0 x =2/7

I was wondering why does squaring get rid of the mod signs?

In the mark scheme there is another method in which

6x - 1 = -x +1

What is this method all about??
(edited 10 years ago)
Original post by IShouldBeRevising_
Thats incorrect... Im not thinking of it like this you would be right if the equation was 10 -x^2... I think anyway lol



Yeah sorry guys it was suppose to be a 10...

and yes this in june 05

btw can you anybody help with this question I have

| 6x - 1 | = | x - 1 |

Basically I squared both sides as squaring gets rid of both mod signs and solved the quadratic and obtained x = 0 x =2/7

I was wondering why does squaring get rid of the mod signs?

In the mark scheme there is another method in which

6x - 1 = -x +1

What is this method all about??


It's not incorrect, I just did this paper. The question asks for the RANGE not the maximum point. The range will be f(x)<_ 10.

You should notice the form the quadratic is in. It's an upside down parabola with the mid point at (-3,10)

Squaring gets right of mod signs because they're just the magnitude of the number hence it must be positive. Squaring a number will ALWAYS be positive. Hence squaring mod eradicates the possibly of them being negative.
Original post by eggfriedrice
It's not incorrect, I just did this paper. The question asks for the RANGE not the maximum point. The range will be f(x)<_ 10.

You should notice the form the quadratic is in. It's an upside down parabola with the mid point at (-3,10)

Squaring gets right of mod signs because they're just the magnitude of the number hence it must be positive. Squaring a number will ALWAYS be positive. Hence squaring mod eradicates the possibly of them being negative.


oh ok thanks mate... any idea about the other method?

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