Processing Math: Done

From Förberedande kurs i matematik 1

Instead of randomly trying different values of x, it is better investigate the second-degree expression by completing the square,

4x2−28x+48=4(x2−7x+12)=4(x−27)2−(27)2+12=4(x−27)2−449+448=4(x−27)2−41=4x−272−1.

In the expression in which the square has been completed, we see that if, e.g. x=72, then the whole expression is negative and equal to -1.

Note: All values of x between 3 and 4 give a negative value for the expression.