GCSE Edexcel Maths Unit 3 19/06/2012 Exam Discussion

Original post by cleveradam

Melissa i need around a High 'C' to low 'B' for an overall B, how many raw marks would you think that'd roughly be?

im not to sure sorry

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what do we need to know about loci i've never heard of it

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Original post by Melissajanex

How do you complete the square anyone ? :smile:

If a quadratic expression is written in the form (x + p)² + q it is in the 'completed square form'.

So far, the only way I've come across for completing the square is by using the formula
x² + 2bx + c = (x + b)² - b ² + c

-----------------------------------------------------------

Here's a question where this formula can be used:

Write x² + 6x + 20 in the form (x + p)² + q

Firstly, look at the formula for completing the square. 2b = 6 so b = 3, and c is 20. Then, substitute these values into the formula.

x² + 6x + 20 = (x + 3)² - 3² + 20
= (x + 3)² - 9 + 20
= (x + 3)² + 11

And that's it! Just find what you need in your original question, and substitute it into the formula given, and voila, there we go!
There is probably 100 other ways of explaining this, but I've got my text book open in front of me and this is what it says :P
Good luck!

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Original post by another_member

Wouldn't it be -8x + 5x which would = -3x not positive 3x?

Nope

Reply 287

Original post by another_member

Wouldn't it be -8x + 5x which would = -3x not positive 3x?

I think it's positive 3x because you're subtracting the 5x from the left hand side from the 8x on the right hand side, and 8x - 5x = 3x :P

Reply 288

Original post by Bixel

If a quadratic expression is written in the form (x + p)² + q it is in the 'completed square form'.

So far, the only way I've come across for completing the square is by using the formula
x² + 2bx + c = (x + b)² - b ² + c

-----------------------------------------------------------

Here's a question where this formula can be used:

Write x² + 6x + 20 in the form (x + p)² + q

Firstly, look at the formula for completing the square. 2b = 6 so b = 3, and c is 20. Then, substitute these values into the formula.

x² + 6x + 20 = (x + 3)² - 3² + 20
= (x + 3)² - 9 + 20
= (x + 3)² + 11

And that's it! Just find what you need in your original question, and substitute it into the formula given, and voila, there we go!
There is probably 100 other ways of explaining this, but I've got my text book open in front of me and this is what it says :P
Good luck!

Thankyou so much! do you know what we have to know about loci?

Reply 289

Original post by Melissajanex

Thankyou so much! do you know what we have to know about loci?

No problem! I think Loci is stupidly easy - it's basically questions where will be asked to shade about a region that satisfies more than one condition.

Remember the questions where it says things like "points in the shaded region are closer to B than C"? It's a really really easy subject, one of which is more common sense than maths, so don't worry about this!

Reply 290

rory58824

2

Original post by Bixel

How about this one, here is a good question on percentages!
Susie bought a car two years ago. It depreciated by 10% each year. The car is now worth £8100. Work out the original cost of Susie's car.

If the car depreciates over two years with the same percentage, we can square the percentage loss. (0.9^2 = 0.81)

Let x = the price before the depreciation.

Therefore 0.81x = 8100
Therefore x = 10000

The price of the car before the loss was £10,000.

(I'm so up for this, bring it on Edexcel!)

What is q*3 + q*4?

Got two questions on upper and lower bounds - probably easy but I saw one of you asked about them...

1. A fence is 22m long to the nearest metre. What are the upper and lower bounds?

2. A box is 8.5cm wide measured to the nearest tenth of a cm. What are the upper and lower bounds?

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Original post by hypanx

What is q*3 + q*4?

q*7?

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Original post by rory58824

Got two questions on upper and lower bounds - probably easy but I saw one of you asked about them...

1. A fence is 22m long to the nearest metre. What are the upper and lower bounds?

2. A box is 8.5cm wide measured to the nearest tenth of a cm. What are the upper and lower bounds?

1) Upper: 22.5m Lower: 21.5m
2) Upper: 8.55cm Lower: 8.45cm
I very much HOPE that is correct, Upper/Lower bounds are on my "Must Work On" list for tonight/tomorrow morning!

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