# Cambridge Prelim MX1 Textbook Marathon/Q&A (1 Viewer)

#### appleibeats

##### Member
Though of starting this thread to help preliminary students with their struggle with any maths problems from this book only, especially with the extension questions.

If you are asking a question, remember to reference which question it is in the book.
If you are going to post an answer, please show full working out.

Thanks.

#### MilkyCat_

##### Active Member

Maths in Focus lyf

#### appleibeats

##### Member

I guess I will be the first to ask.

Does anyone know how to answer question 16 i and k in Exercise 4F. Thanks.

#### appleibeats

##### Member

FYI I tried to write the question up here, but encountered some difficulties. I guess that means you need the book to help answer. Thanks.

#### Drsoccerball

##### Well-Known Member

FYI I tried to write the question up here, but encountered some difficulties. I guess that means you need the book to help answer. Thanks.
Post the question and i will answer..

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#### Ambility

##### Active Member

Here are the questions he was referring to:
Prove the identities:

16i.)$\bg_white \frac{1}{\cot \theta- \cos \theta} = \frac{\tan \theta}{1-\sin \theta} = \frac{\sin \theta + \sin^2 \theta}{\cos^3 \theta}$

16k.)$\bg_white \frac{(\sin^2\alpha-\cos^2\alpha)(1-\sin\alpha\cos\alpha)}{\cos\alpha(\sec\alpha-\csc\alpha)(\sin^3\alpha+\cos^3\alpha)} = \sin\alpha$

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#### barcyy

##### Member

im having troubles with solving inequations with a variable in the denominator - 3A any help will be greatly appreciated!

#### enigma_1

##### ~~~~ Miss Cricket ~~~~

Maths in Focus lyf
Don't use Maths in focus

#### enigma_1

##### ~~~~ Miss Cricket ~~~~

im having troubles with solving inequations with a variable in the denominator - 3A any help will be greatly appreciated!
Do you mean something like the example on page 75?

If there's a variable inn the denominator, the reason that you have to multiply both sides by the square of the denominator if it has a variable like "x" in it is to ensure that you're multiplying both sides by a positive number (since if you square something, either positive/negative it will always be positive) and hence there will be no need to be confused about whether to switch the inequality sign. Coz you know howif you multiply/divide both sides of an inequality by a negative number, the sign flips yeah? So that's why.

When you do that, you get like a quadratic/cubic or whatever which you can then factorise. Then you graph it as a parabola/cubic or whatever it may be. (ie if the quadratic is greater than/less than/ greater than or equal to/less than or equal to ZERO. And then you apply the inequality to the graph and determine what the final inequality will be from the graph.

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#### Meight

##### New Member

Oops lol didn't see this thread...
Well here are a few questions for simple plane geometry. I don't know the 'proper' way of doing these questions and there's no answers to refer to in the back.
It's from Exercise 8B [Question 12. (a),(b),(c),(d)]
View attachment 31895

#### WrittenLoveLetters

##### 배고파

Don't use Maths in focus
School assigns Maths in Focus T___T

#### appleibeats

##### Member

Hi, not sure how to go about question 16 from chapter 4J. The question is

the side of a triangle are n2 + n + 1 , 2n + 1 and n2 - 1, where n>1. Find the largest angle of the triangle.

( n2 being --> n squared )

Thanks.

#### Ambility

##### Active Member

Oops lol didn't see this thread...
Well here are a few questions for simple plane geometry. I don't know the 'proper' way of doing these questions and there's no answers to refer to in the back.
It's from Exercise 8B [Question 12. (a),(b),(c),(d)]
View attachment 31895
In my book, question 12 only has an ai, aii, aiii, aiv, av and b. Are you sure your talking about the right question?

#### Meight

##### New Member

Oops... it's from the year 12 3 unit cambridge textbook, not the year 11 one.

#### happy_turtle

##### New Member

Don't use Maths in focus
What's wrong with maths in focus?

#### Ambility

##### Active Member

What's wrong with maths in focus?
A lot of people say Maths in Focus is too easy for the subject its designed for - that it doesn't challenge students enough. Most of these people say cambridge is a good alternative. I, however, own and use both books and I find that they are both good for separate uses. Maths in Focus is great for introducing you to the concepts and ideas, and it does this so well that it is quite easy to catch up if you have missed a lesson, while cambridge really allows you to develop your skills and apply them to harder, or more abstract problems.

#### enigma_1

##### ~~~~ Miss Cricket ~~~~

School assigns Maths in Focus T___T
What's wrong with maths in focus?
it's a terrible book. Use Cambridge instead. Make Maths in focus extinct from your lives pls

ty

#### appleibeats

##### Member

Having troubles with question 15 b from 6A.

The question is :

Write as a single fraction, without negative indices, and simplify:

1 - y^ -1 divided by 1 - y^-2

#### Ambility

##### Active Member

Having troubles with question 15 b from 6A.

The question is :

Write as a single fraction, without negative indices, and simplify:

1 - y^ -1 divided by 1 - y^-2
Generally with these questions, if you can get as much as possible under a common denominator, then invert and multiply, you should be sweet.

$\bg_white 1-y^{-1} \div 1-y^{-2}\\=1-\frac{1}{y}\div1-\frac{1}{y^2}\\=\frac{y}{y}-\frac{1}{y}\div\frac{y^2}{y^2}-\frac{1}{y^2}\\=\frac{y-1}{y}\div\frac{y^2-1}{y^2}\\\text{Now, we invert and multiply:}\\=\frac{y-1}{y}\times\frac{y^2}{y^2-1}\\=\frac{y^3-y^2}{y^3-y}\\\text{Now, we simplify:}\\\frac{y^2-y}{y^2-1}$