Solving equations and inequalities: Linear inequalities in one unknown
Reduction to a linear inequality
In some cases, you can reduce complicated inequalities to linear inequalities.
We note first that division by zero is not allowed and that for this reason \(7x+6\) may not be equal to zero and that therefore \(x=-{{6}\over{7}}\) is not a solution.
We now distinguish two cases, namely \(7x+6>0\) and \(7x+6<0\).
In both cases we multiply the inequality on both sides by \(7x+6\) because we then get a linear inequality, for which we know there is a solution method.
Suppose \(7x+6>0\), i.e. \(x> -{{6}\over{7}}\). Then we get \(2<-7(7x+6)\).
When we move everything with \(x\) to the left and all constant terms to the right, we get \(49x<-44\).
Then, dvision by the coefficient of \(x\)gives \(x < -{{44}\over{49}}\).
So we have the following system of inequalities: \(x> -{{6}\over{7}}\,\wedge\; x < -{{44}\over{49}}\)
and this simplifies to \(\text{an empty solution set}\).
Suppose \(7x+6<0\), i.e. \(x< -{{6}\over{7}}\). Then we get \(2>-7(7x+6)\).
When we move everything with \(x\) to the left and all constant terms to the right, we get \(49x>-44\).
Then, division by the coefficient of \(x\) gives \(x > -{{44}\over{49}}\).
So we have the following system of inequalities: \(x< -{{6}\over{7}}\,\wedge\; x > -{{44}\over{49}}\)
and this simplifies to \(-{{44}\over{49}}\lt x\lt -{{6}\over{7}}\).
The solution of the original inequality is \(-{{44}\over{49}}\lt x\lt -{{6}\over{7}}\).