Solutions to Inequalities in One Variable

Student Summary

The equation 12t=10\frac12 t = 10 is an equation in one variable. Its solution is any value of tt that makes the equation true. Only t=20t=20 meets that requirement, so 20 is the only solution.

The inequality 12t>10\frac12t >10 is an inequality in one variable. Any value of tt that makes the inequality true is a solution. For instance, 30 and 48 are both solutions because substituting these values for tt produces true inequalities. 12(30)>10\frac12(30) >10 is true, as is 12(48)>10\frac12(48) >10. Because the inequality has a range of values that make it true, we sometimes refer to all the solutions as the solution set.

One way to find the solutions to an inequality is by reasoning. For example, to find the solution to 2p<82p<8, we can reason that if 2 times a value is less than 8, then that value must be less than 4. So a solution to 2p<82p<8 is any value of pp that is less than 4.

Another way to find the solutions to 2p<82p<8 is to solve the related equation 2p=82p=8. In this case, dividing each side of the equation by 2 gives p=4p=4. This point, where pp is 4, is the boundary of the solution to the inequality.

To find out the range of values that make the inequality true, we can try values less than and greater than 4 in our inequality and see which ones make a true statement.

Let's try some values less than 4:

  • If p=3p=3, the inequality is 2(3)<82(3) <8 or 6<86 < 8, which is true.
  • If p=-1p=\text-1, the inequality is 2(-1)<82(\text-1) < 8 or -2<8\text-2 <8, which is also true.

Let's try values greater than 4:

  • If p=5p=5, the inequality is 2(5)<82(5)<8 or 10<810<8, which is false.
  • If p=12p=12, the inequality is 2(12)<82(12) <8 or 24<824<8, which is also false.

In general, the inequality is false when pp is greater than or equal to 4 and true when pp is less than 4.

We can represent the solution set to an inequality by writing an inequality, p<4p<4, or by graphing on a number line. The ray pointing to the left represents all values less than 4.

<p>Inequality graphed on a number line. Numbers from negative 6 to 6, by 1’s. At 4, open circle with line extending to the left.</p>

Visual / Anchor Chart

Standards

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