Find Increasing and Decreasing Intervals: y = 2x² - 5x + 3

Find the intervals of increase and decrease of the function:

y=2x25x+3 y=2x^2-5x+3

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find the intervals of increase and decrease of the function
00:03 We'll use the formula to find the X value at the vertex
00:07 Let's identify the trinomial coefficients
00:11 We'll substitute appropriate values according to the given data, and solve for X
00:22 This is the X value at the vertex point
00:28 The coefficient A is positive, therefore the parabola has a minimum point
00:36 From the graph we'll determine the intervals of increase and decrease
00:49 And this is the solution to the question

Step-by-step written solution

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1

Understand the problem

Find the intervals of increase and decrease of the function:

y=2x25x+3 y=2x^2-5x+3

2

Step-by-step solution

To solve this problem, we'll start by differentiating the function:

The given function is y=2x25x+3 y = 2x^2 - 5x + 3 . To find intervals of increase and decrease, we need the first derivative y y' :

y=ddx(2x25x+3)=4x5 y' = \frac{d}{dx}(2x^2 - 5x + 3) = 4x - 5 .

Next, find the critical points by setting y=0 y' = 0 and solving for x x :

4x5=0 4x - 5 = 0
4x=5 4x = 5
x=54 x = \frac{5}{4} .

The critical point is at x=54 x = \frac{5}{4} , which is x=114 x = 1\frac{1}{4} in mixed fraction form.

Now, determine where the function is increasing or decreasing by analyzing the sign of y=4x5 y' = 4x - 5 :

  • For x<54 x < \frac{5}{4} , y=4x5<0 y' = 4x - 5 < 0 , indicating the function is decreasing.
  • For x>54 x > \frac{5}{4} , y=4x5>0 y' = 4x - 5 > 0 , indicating the function is increasing.

Therefore, the intervals of increase and decrease are:

  • Decreasing for x<114 x < 1\frac{1}{4} .
  • Increasing for x>114 x > 1\frac{1}{4} .

The correct answer is the interval description:

 :x<114   :x>114 \searrow~:x < 1\frac{1}{4}~~ \\ \nearrow~:x > 1\frac{1}{4} .

3

Final Answer

 :x<114   :x>114 \searrow~:x < 1\frac{1}{4}~~\\ \nearrow~:x>1\frac{1}{4}

Practice Quiz

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Note that the graph of the function shown below does not intersect the x-axis

The parabola's vertex is A

Identify the interval where the function is decreasing:

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