Locate the Vertex of the Quadratic Function f(x) = 3x^2 + 6x

Vertex Formula with Coordinate Calculation

Given the expression of the quadratic function

Finding the symmetry point of the function

f(x)=3x2+6x f(x)=3x^2+6x

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:08 Let's find the symmetry point of a function.
00:11 The symmetry point is where, if you fold the parabola, it lines up perfectly.
00:17 Both sides will match exactly.
00:20 First, we'll look at the function's coefficients.
00:24 We'll use a formula to find the vertex point.
00:28 Plug in the given values, and solve for X, the symmetry point.
00:33 This gives us the X value of the symmetry point.
00:37 Next, substitute this X into the function to find the Y value.
00:50 Remember, negative numbers squared are always positive.
01:03 This Y value is part of the symmetry point.
01:07 And that's how we solve the problem.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Given the expression of the quadratic function

Finding the symmetry point of the function

f(x)=3x2+6x f(x)=3x^2+6x

2

Step-by-step solution

To find the symmetry point of the quadratic function f(x)=3x2+6x f(x) = 3x^2 + 6x , follow these steps:

  • Step 1: Identify the coefficients from the quadratic function ax2+bx+c ax^2 + bx + c . Here, a=3 a = 3 and b=6 b = 6 .
  • Step 2: Use the vertex formula for the symmetry point, which is given by x=b2a x = -\frac{b}{2a} .
  • Step 3: Substitute the values of a a and b b into the formula:

x=62×3=66=1 x = -\frac{6}{2 \times 3} = -\frac{6}{6} = -1

  • Step 4: Substitute x=1 x = -1 back into the original function to find the corresponding y y -coordinate:

f(1)=3(1)2+6(1)=3×16=36=3 f(-1) = 3(-1)^2 + 6(-1) = 3 \times 1 - 6 = 3 - 6 = -3

  • Step 5: Therefore, the symmetry point of the function is (1,3)(-1, -3).

Thus, the symmetry point of the given quadratic function f(x)=3x2+6x f(x) = 3x^2 + 6x is (1,3)\boxed{(-1, -3)}.

3

Final Answer

(1,3) (-1,-3)

Key Points to Remember

Essential concepts to master this topic
  • Formula: Use x=b2a x = -\frac{b}{2a} to find x-coordinate of vertex
  • Technique: With a=3,b=6 a = 3, b = 6 : x=62(3)=1 x = -\frac{6}{2(3)} = -1
  • Check: Substitute x back: f(1)=3(1)2+6(1)=3 f(-1) = 3(-1)^2 + 6(-1) = -3

Common Mistakes

Avoid these frequent errors
  • Using wrong sign in vertex formula
    Don't forget the negative sign in x=b2a x = -\frac{b}{2a} = wrong x-coordinate! Students often calculate x=66=1 x = \frac{6}{6} = 1 instead of x=66=1 x = -\frac{6}{6} = -1 . Always include the negative sign before the fraction.

Practice Quiz

Test your knowledge with interactive questions

Given the expression of the quadratic function

Finding the symmetry point of the function

\( f(x)=-5x^2+10 \)

FAQ

Everything you need to know about this question

Why is the vertex formula x=b2a x = -\frac{b}{2a} ?

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This formula comes from completing the square or using calculus. The vertex occurs at the axis of symmetry, which is exactly halfway between the roots of the quadratic.

What if there's no c term like in this problem?

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That's fine! When c=0 c = 0 , the parabola passes through the origin. You still use the same vertex formula with a and b coefficients only.

How do I remember which coordinate is which?

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Think "x first, then y"! Find the x-coordinate using the formula, then substitute that x-value back into the original function to get the y-coordinate.

What does the vertex tell me about the parabola?

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The vertex is the turning point! Since a=3>0 a = 3 > 0 , this parabola opens upward, so (1,3) (-1, -3) is the lowest point.

Can I check my answer another way?

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Yes! The vertex should be equidistant from any two points with the same y-value. You can also verify that x = -1 is the axis of symmetry by checking that the parabola is symmetric around this line.

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