NZ Level 6 (NZC) Level 1 (NCEA)
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One step inequalities on a number line
Lesson

As we have previously seen, we can plot inequalities by using number lines.

For example, a plot of the inequality $x\le4$x4 looks like this:

 

Now let's consider an inequality such as $x+3>5$x+3>5. What would we plot for this inequality?

As in the case of $x\le4$x4 above, what we want to plot on the number line are all of the possible values that the variable can take - that is, the solutions of the inequality. The inequality $x+3>5$x+3>5 has the solutions "all numbers which, when added to $3$3 result in a number greater than $5$5". This is a little bit of a mouthful already, and there are definitely much more complicated inequalities than this!

So in order to plot the solutions to an inequality such as $x+3>5$x+3>5, it will be easiest to first solve the inequality. In this case, we can subtract $3$3 from both sides to get $x>2$x>2. So the plot will show "all numbers greater than $2$2" on the number line, which looks like this:

 

Remember

When solving an inequality:

  • Multiplying or dividing both sides by a negative number will reverse the inequality symbol.
  • Reversing the order of the inequality will reverse the inequality symbol too.

When plotting an inequality:

  • The symbols $<$< and $>$> don't include the end point, which we show with a hollow circle.
  • The symbols $\ge$ and $\le$ do include the endpoint, which we show with a filled circle.

 

Practice Questions

Question 1

Consider the inequality $3+x<2$3+x<2.

  1. Solve the inequality.

  2. Now plot the solutions to the inequality $3+x<2$3+x<2 on the number line below.

    -10-50510

Question 2

Consider the inequality $2x>-4$2x>4.

  1. Solve the inequality.

  2. Now plot the solutions to the inequality $2x>-4$2x>4 on the number line below.

    -10-50510

Question 3

Consider the inequality $\frac{x}{-7}<2$x7<2.

  1. Solve the inequality.

  2. Now plot the solutions to the inequality $\frac{x}{-7}<2$x7<2 on the number line below.

    -20-15-10-505101520

Outcomes

NA6-7

Relate graphs, tables, and equations to linear, quadratic, and simple exponential relationships found in number and spatial patterns

91028

Investigate relationships between tables, equations and graphs

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