Solving Linear Inequalities Lesson
When we have to solve a linear inequlity all we have to do is graph the line like we do for a normal linear equation,
For example : y > 4x - 2 We just graph the line, like we normally would (we use a dotted line since the sign is > not >=). Then we would shade in the arae above the line since y is greater then that y value on the line. y <= -2x - 3 For this one we graph the line with a solid line, since y may be equal to the y value at that point on the line. We then shade the area below the line (all values of y less than the value on the line). 4x + 4y > 8 We first have to solve for y. y > -1x + 2. Then graph the area above that line. To test to see if it works pick a point in the shaded area. Let's try (5,5). Does it work? 5 > -1(5) + 2 Yes, it works. So we have shaded the right area. The only tricky thing with solving these equations is that we have to flip the sign of the inequality if we multiply or divide by a negative number, when we are solving the equation. For example : -2y - 2x > 4 -2y > 2x + 4 y < -1x - 2 Notice : we had to flip the sign when we divided by the -2. Graph the area under the line. Check a point in the shaded area, say point (-5,-5). It works in both our original equation and our new one, so we have shaded the correct side. Look at : -1x > 5 we can see that only negative numbers would work to solve this inequality. If we divide by -1 we get x > -5 and we see that our solution set is now wrong. Flipping the sign we get x < -5 and our solution set is now correct. Look at -1/2x >= 4 We can see that our solution set has to be a negative number. Multiplying both sides by -2 gives us : x >= -8 which doesn't give us the correct result. Flipping the sign gives us : x <= 8 which gives us the correct result. |