Solving (x-1/2)(x+6.5): Finding Negative Function Values

Question

Find the positive and negative domains of the following function:

y=(x12)(x+612) y=\left(x-\frac{1}{2}\right)\left(x+6\frac{1}{2}\right)

Determine for which values of x x the following is true:

f(x) < 0

Step-by-Step Solution

Let us solve the problem step by step to find: x x values for which f(x) < 0 .

Firstly, identify the roots of the function y=(x12)(x+612) y = \left(x - \frac{1}{2}\right)\left(x + 6\frac{1}{2}\right) :

  • The root from (x12)=0 \left(x - \frac{1}{2}\right) = 0 is x=12 x = \frac{1}{2} .
  • The root from (x+612)=0 \left(x + 6\frac{1}{2}\right) = 0 is x=612 x = -6\frac{1}{2} .

These roots divide the real number line into three intervals:

  • x<612 x < -6\frac{1}{2}
  • 612<x<12 -6\frac{1}{2} < x < \frac{1}{2}
  • x>12 x > \frac{1}{2}

To determine where the function is negative, evaluate the sign in each interval:

  • For x<612 x < -6\frac{1}{2} : Both factors (x12) (x - \frac{1}{2}) and (x+612) (x + 6\frac{1}{2}) are negative, so their product is positive.
  • For 612<x<12 -6\frac{1}{2} < x < \frac{1}{2} : (x12) (x - \frac{1}{2}) is negative and (x+612) (x + 6\frac{1}{2}) is positive, thus the product is negative.
  • For x>12 x > \frac{1}{2} : Both factors are positive, so their product is positive.

Hence, the function is negative on the interval: 612<x<12 -6\frac{1}{2} < x < \frac{1}{2} .

Answer

-6\frac{1}{2} < x < \frac{1}{2}