Sign charts are usefull to solve inequalities. Read carefully the following examples, it will help you understand : *** How to solve . If both factors in a product are positive (or negative), then the product is positive too. Hence the sign of (2 x - 2)(4 x + 16) depends on the sign of its two factors. Let's find the signs of the two factors thanks to 2 equations : On the last line, we can see that whenever . -4 and 1 are excluded from the set of solutions because the inequality can't be an equality. *** How to solve It is the same thing, the sign of a quotient depends on the sign of the numerator and the sign of the denominator. There is just a difference : you can't divide by zero. So you draw a double bar in the table, under the "forbidden" value. 5 is excluded from the set of solutions. When there is a double bar, the value below is always excluded from the set of solutions. In that case, we are looking for negative or null values ; finally, the solutions are : . *** How to solve |