# Past Papers’ Solutions | Cambridge International Examinations (CIE) | AS & A level | Mathematics 9709 | Pure Mathematics 2 (P2-9709/02) | Year 2003 | May-Jun | (P2-9709/02) | Q#1

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Question

Solve the inequality .

Solution

SOLVING INEQUALITY: PIECEWISE

Let, . We can write it as;

We have to consider both moduli separately and it leads to following cases;

 When

If then above four intervals translate to following with their corresponding inequality;

 When When When

If then above four intervals translate to following with their corresponding inequality;

 When When When

We have the inequality;

In standard form it can be written as;

We have to consider both moduli separately and it leads to following cases;

Since then above four intervals translate to;

We can see that given inequality takes following forms for these intervals.

 For interval For interval For interval No value of  can be found from this inequality, hence, no solution of given inequality exists for this interval. No value of  can be found from this inequality, hence, no solution of given inequality exists for this interval.

Hence, the only solution for the given inequality is;

SOLVING INEQUALITY: ALGEBRAICALLY

Let, .

Since given equation/inequality is of the form  or  or ,  we can solve this inequality by taking square of both sides;

We are given inequality;

Therefore, we can solve it algebraically;

Hence, the only solution for the given inequality is;

SOLVING INEQUALITY: GRAPHICALLY

We are given inequality;

To solve the inequality graphically, we need to sketch both sides of inequality;

Let’s sketch both equations one-by-one.

First we have to sketch;

Let, .

It can be written as;

We have to draw two separate graphs;

 When ; When ; Therefore; Therefore;

It is evident that  and are reflection of each other in x-axis. So we can  draw line of by first drawing and then reflecting in x-axis that part of the line  which is below x-axis.

We have to draw two separate graphs;

 When ; When ; Therefore; Therefore;

It is evident that and are reflection of each other in x-axis. So we can sketch  by first drawing and then reflecting in x-axis that part of the line which  is below x-axis.

Therefore, first we sketch the line .

To sketch a line we only need x and y intercepts of the line.

The point at which curve (or line) intercepts x-axis, the value of . So we can find the  value of coordinate by substituting in the equation of the curve (or line).

Therefore, we substitute in given equation of the line.

Hence, coordinates of x-intercept of the line with are .

The point at which curve (or line) intercepts y-axis, the value of . So we can find the  value of coordinate by substituting in the equation of the curve (or line).

Therefore, we substitute in given equation of the line.

Hence, coordinates of y-intercept of the line with are .

Hence, we get following graph for ;

We can reflect in x-axis that part of the line which is below x-axis to make it graph of , as
shown below.

Now we have to sketch;

Let, .

It can be written as;

We have to draw two separate graphs;

 When ; When ; Therefore; Therefore;

It is evident that  and are reflection of each other in x-axis. So we can  draw line of by first drawing and then reflecting in x-axis that part of the line which is below x-axis.

It can be written as;

We have to draw two separate graphs;

 When ; When ; Therefore; Therefore;

It is evident that  and are reflection of each other in x-axis. So we can sketch  by first drawing and then reflecting in x-axis that part of the line which is  below x-axis.

Therefore, next we sketch the line .

To sketch a line we only need x and y intercepts of the line.

The point at which curve (or line) intercepts x-axis, the value of . So we can find the  value of coordinate by substituting in the equation of the curve (or line).

Therefore, we substitute in given equation of the line.

Hence, coordinates of x-intercept of the line with are .

The point at which curve (or line) intercepts y-axis, the value of . So we can find the  value of coordinate by substituting in the equation of the curve (or line).

Therefore, we substitute in given equation of the line.

Hence, coordinates of y-intercept of the line with are .

Hence, we get following graph for ;

We can reflect in x-axis that part of the line which is below x-axis to make it graph of , as shown below.

When we sketch the two graphs on the same axes and we get following.

We are looking for the solution of .

It is evident from the graphs that is above (greater) than for all values of;