GRE Subject Test: Math : Inequalities

Example Questions

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Example Question #1 : Solving Inequalities

Given the following inequality, find

Explanation:

Before we get started, read the question carefully. We need to find x squared, not x. Don't call it quits too early!

So, we start here:

Get the x's on one side and the constants on the other.

When we divide by a negative number in an inequality, remember that we need to switch the direction of the sign.

Example Question #1 : Inequalities

Solve the inequality for .

Explanation:

We can either divide the other side of the inequality by  or distribute it. We'll go ahead and distribute it here:

Now we just solve:

Example Question #1 : Inequalities

If , what is the largest integer of  for which

Explanation:

The first thing we must do is solve the given equation for

Since we are looking for values when , we can set up our equation as follows:

Solve.

So,  is the largest integer of x which makes the statement true.

Example Question #4 : Solving Inequalities

If , what is the smallest integer of  for which ?

Explanation:

Our first step will be to solve the given equation for :

Since we want to know the smallest integer of  for which , we can set up our equation as

Example Question #5 : Solving Inequalities

Explanation:

This problem requires first combining like terms that are on opposite sides of the inequality.

First add 3x to both sides of the inequality to get

.

Then subtract 2 from both sides.

Now, divide 7 from both sides to get x alone.

which you should switch the order to be

.

Example Question #1 : Quadratic Inequalities

Solve the following inequality

No Solution

All Real Numbers

Explanation:

We begin by moving all of our terms to the left side of the inequality.

We then factor.

That means our left side will equal 0 when .  However, we also want to know the values when the left side is less than zero.  We can do this using test regions.  We begin by drawing a number line with our two numbers labeled.

We notice that our two numbers divide our line into three regions.  We simply need to try a test value in each region.  We begin with our leftmost region by selecting a number less than .  We then plug that value into the left side of our inequality to see if the result is positive or negative.  Any value (such as ) will give us a positive value.

We then repeat this process with the center region by selecting a value between our two numbers.  Any value (such as ) will result in a negative outcome.

Finally we complete the process with the rightmost region by selecting a value larger than .  Any value (such as ) will result in a positive value.

We then label our regions accordingly.

Since we want the result to be less than zero, we want the values between our two numbers.  However, since our left side can be less than or equal to zero, we can also include the two numbers themselves.  We can express this as

Example Question #2 : Quadratic Inequalities

Explanation:

We begin by solving the equation for its zeros. This is done by changing the  sign into an  sign.

Since we know the zeros of the equation, we can then check the areas around the zeros since we naturally have split up the real line into three sections :

First we check

Therefore, the first interval can be included in our answer. Additionally, we know that  satisfies the equation, therefore we can say with certainty that the interval  is part of the answer.

Next we check something in the second interval. Let , then

Therefore the second interval cannot be included in the answer.

Lastly, we check the third interval. Let , then

Which does satisfy the original equation. Therefore the third interval can also be included in the answer. Since we know that  satisfies the equation as well, we can include it in the interval as such:

Therefore,

Example Question #3 : Quadratic Inequalities

Solve:

Explanation:

Method 1:

1) Multiply-out the left side then rewrite the inequality as an equation:

2) Now rewrite as a quadratic equation and solve the equation:

3) Next set up intervals using the solutions and test the original inequality to   see where it holds true by using values for  on each interval.

4) The interval between  and  holds true for the original inequality.

5) Solution:

Method 2:

Using a graphing calculator, find the graph.  The function is below the x-axis (less than ) for the x-values .  Using interval notation for , .

Method 3:

For the inequality , the variable expression in terms of is less than , and an inequality has a range of values that the solution is composed of.  This means that each of the solution values for  are strictly between the two solutions of .  'Between' is for a 'less than' case, 'Outside of' is for a 'greater than' case.

Example Question #1 : Inequalities

Explanation:

Subtract 9 from both sides of the inequality.

Because the variable, in this case  is to the right of the inequality sign, you switch the inequality sign to its opposite.  The  becomes a  so that the variable is to the left of the inequality sign.