Determine X for Positive Values in the Quadratic Equation y = 3x² - 6x + 4

Quadratic Functions with Negative Discriminants

Look at the following function:

y=3x26x+4 y=3x^2-6x+4

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

f(x)>0 f\left(x\right)>0

❤️ Continue Your Math Journey!

We have hundreds of course questions with personalized recommendations + Account 100% premium

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Look at the following function:

y=3x26x+4 y=3x^2-6x+4

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

f(x)>0 f\left(x\right)>0

2

Step-by-step solution

To solve the problem, we'll follow these steps:

  • Step 1: Solve the quadratic equation 3x26x+4=0 3x^2 - 6x + 4 = 0 using the quadratic formula.
  • Step 2: Determine the intervals based on the roots and analyze the sign of the quadratic in each interval.
  • Step 3: Use the results to conclude for which values of x x the quadratic is positive.

Step 1: The quadratic formula yields the roots:

x=b±b24ac2a,x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}, where a=3 a = 3 , b=6 b = -6 , and c=4 c = 4 .

Calculating the discriminant:

b24ac=(6)2434=3648=12 b^2 - 4ac = (-6)^2 - 4 \cdot 3 \cdot 4 = 36 - 48 = -12 .

Since the discriminant is negative (12-12), the quadratic equation has no real roots. This means the parabola does not intersect the x-axis, and the entire graph is above or below it.

Step 2: Since a=3 a = 3 (positive), the parabola opens upwards. A quadratic function with no real roots and a positive leading coefficient will be entirely above the x-axis, indicating it is always greater than zero.

Step 3: Since it is positive across all x x -values, the solution is:

The function is positive for all x x .

3

Final Answer

The function is positive for all x x .

Key Points to Remember

Essential concepts to master this topic
  • Discriminant Rule: When b24ac<0 b^2 - 4ac < 0 , no real roots exist
  • Technique: Calculate (6)24(3)(4)=3648=12 (-6)^2 - 4(3)(4) = 36 - 48 = -12
  • Check: Positive leading coefficient with no roots means always positive ✓

Common Mistakes

Avoid these frequent errors
  • Assuming negative discriminant means no solution
    Don't think negative discriminant = no solution to f(x) > 0! This only means no x-intercepts exist. The parabola still has values - it's entirely above or below the x-axis. Always check the leading coefficient to determine if the function is always positive or always negative.

Practice Quiz

Test your knowledge with interactive questions

The graph of the function below intersects the X-axis at points A and B.

The vertex of the parabola is marked at point C.

Find all values of \( x \) where \( f\left(x\right) > 0 \).

AAABBBCCCX

FAQ

Everything you need to know about this question

What does it mean when the discriminant is negative?

+

A negative discriminant means the parabola never touches the x-axis. It's either completely above or below the x-axis, depending on whether it opens up or down.

How do I know if the parabola opens up or down?

+

Look at the leading coefficient (the number in front of x2 x^2 ). If it's positive, the parabola opens upward. If negative, it opens downward.

Why is the function always positive when a > 0 and discriminant < 0?

+

When a > 0, the parabola opens upward. With no real roots, it never touches the x-axis. Since it opens upward and never touches the x-axis, the entire graph must be above the x-axis!

What if the leading coefficient was negative instead?

+

If a<0 a < 0 with a negative discriminant, the parabola would open downward and never touch the x-axis. This means it would be always negative, so f(x) > 0 would have no solution.

Do I still need to use the quadratic formula if the discriminant is negative?

+

You don't need to finish the quadratic formula calculation! Once you see the discriminant is negative, you know there are no real roots. Just check the leading coefficient to determine the sign.

🌟 Unlock Your Math Potential

Get unlimited access to all 18 The Quadratic Function questions, detailed video solutions, and personalized progress tracking.

📹

Unlimited Video Solutions

Step-by-step explanations for every problem

📊

Progress Analytics

Track your mastery across all topics

🚫

Ad-Free Learning

Focus on math without distractions

No credit card required • Cancel anytime

More Questions

Click on any question to see the complete solution with step-by-step explanations