Identifying the Vertex of y=x²+2x: Finding Minimum or Maximum?

Quadratic Functions with Vertex Analysis

Does the parable

y=x2+2x y=x^2+2x

Is there a minimum or maximum point?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Does the parabola have a maximum or minimum point?
00:07 The coefficient A of the function is positive, therefore the parabola smiles
00:16 This means the parabola has a minimum point
00:19 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Does the parable

y=x2+2x y=x^2+2x

Is there a minimum or maximum point?

2

Step-by-step solution

To determine whether the quadratic function y=x2+2x y = x^2 + 2x has a minimum or maximum point, we need to examine its structure and calculate the vertex.

Step 1: Identify the structure of the quadratic function.

The given function is y=x2+2x y = x^2 + 2x , which is a standard form quadratic function y=ax2+bx+c y = ax^2 + bx + c where a=1 a = 1 , b=2 b = 2 , and c=0 c = 0 .

Step 2: Calculate the vertex.

The vertex of a quadratic function is given by x=b2a x = -\frac{b}{2a} . Substituting the values of a a and b b into this formula gives:

x=22×1=1 x = -\frac{2}{2 \times 1} = -1 .

Substitute x=1 x = -1 back into the original equation to find the y-coordinate of the vertex:

y=(1)2+2(1)=12=1 y = (-1)^2 + 2(-1) = 1 - 2 = -1 .

Therefore, the vertex is at the point (1,1)(-1, -1).

Step 3: Determine if the vertex is a minimum or maximum.

Since the coefficient a=1 a = 1 is positive, the parabola opens upwards. This means that the vertex represents the lowest point on the graph, which is a minimum point.

Therefore, the solution to this problem is that the parabola has a minimal point.

3

Final Answer

Minimal point

Key Points to Remember

Essential concepts to master this topic
  • Coefficient Rule: Positive a-value means parabola opens upward with minimum
  • Vertex Formula: Use x=b2a=22(1)=1 x = -\frac{b}{2a} = -\frac{2}{2(1)} = -1
  • Check: Substitute x = -1: y = (-1)² + 2(-1) = -1 ✓

Common Mistakes

Avoid these frequent errors
  • Confusing sign of coefficient with vertex type
    Don't think negative coefficient of x means maximum = wrong direction! The linear term's sign doesn't determine min/max. Always check the coefficient of x² (a-value): positive a means minimum, negative a means maximum.

Practice Quiz

Test your knowledge with interactive questions

What is the value of the coefficient \( b \) in the equation below?

\( 3x^2+8x-5 \)

FAQ

Everything you need to know about this question

How do I remember if it's minimum or maximum?

+

Look at the coefficient of x² (the a-value). If it's positive, the parabola opens upward like a smile = minimum point. If it's negative, it opens downward like a frown = maximum point.

Why is the vertex at (-1, -1) and not (1, 1)?

+

The vertex formula is x=b2a x = -\frac{b}{2a} , which gives us x=22(1)=1 x = -\frac{2}{2(1)} = -1 . Then substitute back: y=(1)2+2(1)=12=1 y = (-1)^2 + 2(-1) = 1 - 2 = -1 .

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

+

That's perfectly normal! When c = 0, it just means the parabola passes through the origin region. The vertex calculation works exactly the same way using the formula.

Can I complete the square instead of using the formula?

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Absolutely! Completing the square gives y=(x+1)21 y = (x+1)^2 - 1 , showing the vertex is at (-1, -1). Both methods work, so use whichever you prefer!

How do I know my vertex calculation is correct?

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Always substitute your x-value back into the original equation to find y. Also, check that points on both sides of the vertex give higher y-values for a minimum.

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