Solve (3x+3)(2-x) < 0: Finding Values Where Function is Negative

Question

Look at the following function:

y=(3x+3)(2x) y=\left(3x+3\right)\left(2-x\right)

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

f\left(x\right) < 0

Step-by-Step Solution

To identify the range of x x such that y=(3x+3)(2x)<0 y = (3x + 3)(2 - x) < 0 , we'll follow these steps:

  • Step 1: Find the roots of the equation by solving (3x+3)=0 (3x + 3) = 0 and (2x)=0 (2 - x) = 0 .
  • Step 2: Find the intervals created by these roots.
  • Step 3: Test each interval to determine the sign of the product.

Let's execute each step:

Step 1: Solving the equations:
First root: Set 3x+3=0 3x + 3 = 0 which gives x=1 x = -1 .
Second root: Set 2x=0 2 - x = 0 which gives x=2 x = 2 .

Step 2: The roots divide the real number line into three intervals:

  • x<1 x < -1
  • 1<x<2 -1 < x < 2
  • x>2 x > 2

Step 3: Analyze each interval:

- For x<1 x < -1 : Choose x=2 x = -2 . The expression becomes (3(2)+3)(2(2))=(3)(4)=12 (3(-2) + 3)(2 - (-2)) = (-3)(4) = -12 , which is negative.

- For 1<x<2 -1 < x < 2 : Choose x=0 x = 0 . The expression becomes (3(0)+3)(20)=(3)(2)=6 (3(0) + 3)(2 - 0) = (3)(2) = 6 , which is positive.

- For x>2 x > 2 : Choose x=3 x = 3 . The expression becomes (3(3)+3)(23)=(12)(1)=12 (3(3) + 3)(2 - 3) = (12)(-1) = -12 , which is negative.

Therefore, the function is negative for x<1 x < -1 or x>2 x > 2 .

The solution to this problem is x>2 x > 2 or x<1 x < -1 .

Answer

x > 2 or x < -1