Find the positive and negative domains of the following function:
y=(2x−21)(x−241)
Determine for which values of x the following is true:
f(x) < 0
To solve this problem, we'll follow these steps:
- Step 1: Identify the roots of the quadratic function.
- Step 2: Analyze the intervals between these roots to determine where the function is negative.
- Step 3: Write the final solution as the interval where f(x)<0.
Now, let's work through each step:
Step 1: Determine the roots by solving each factor for zero:
- 2x−21=0⇒2x=21⇒x=41.
- x−241=0⇒x=241.
Thus, the roots are x=41 and x=241.
Step 2: Analyze the intervals determined by the roots x=41 and x=241:
- Interval 1: x<41
- Interval 2: 41<x<241
- Interval 3: x>241
Step 3: Test each interval:
- For interval 1 x<41: Choose x=0. f(0)=(2(0)−21)(0−241)=(−21)(−241)=89>0.
- For interval 2 41<x<241: Choose x=1. f(1)=(2(1)−21)(1−241)=(23)(−45)=−815<0.
- For interval 3 x>241: Choose x=3. f(3)=(2(3)−21)(3−241)=(211)(43)=833>0.
Therefore, the solution to f(x)<0 is found in the interval 41<x<241.
\frac{1}{4} < x < 2\frac{1}{4}