Finding Points A and B on the Quadratic Graph of f(x) = -x^2 + 5x + 6

X-Intercepts with Factoring Method

The following function has been graphed below:

f(x)=x2+5x+6 f(x)=-x^2+5x+6

Calculate points A and B.

BBBAAACCC

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find the coordinates of points A,B
00:03 Note that points A,B are the intersection points with the X-axis
00:10 At the intersection points with X-axis, the Y value must = 0
00:15 Substitute Y = 0 and solve for X values
00:28 Break down into trinomial
00:32 This is the corresponding trinomial
00:36 Find what zeros each factor in the product
00:41 This is one solution
00:48 This is second solution
00:52 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

The following function has been graphed below:

f(x)=x2+5x+6 f(x)=-x^2+5x+6

Calculate points A and B.

BBBAAACCC

2

Step-by-step solution

To solve for the x-intercepts of the function f(x)=x2+5x+6 f(x) = -x^2 + 5x + 6 , we will find the roots of the quadratic equation x2+5x+6=0 -x^2 + 5x + 6 = 0 .

Let's attempt to factor this quadratic equation first. Rewrite the equation as follows:

x2+5x+6=0 -x^2 + 5x + 6 = 0 .

To factor, we look for two numbers that multiply to 6-6 (the product of aa and cc, where a=1a = -1 and c=6c = 6) and add to 55 (the middle coefficient bb).

The numbers that satisfy this condition are 1-1 and 66.

Thus, the quadratic can be factored as:

(x6)(x+1)=0(x - 6)(x + 1) = 0.

Setting each factor equal to zero gives us:

x6=0x - 6 = 0 or x+1=0x + 1 = 0.

Solving these equations, we find:

x=6x = 6 and x=1x = -1.

Thus, the points A and B, the x-intercepts of the function, are:

(1,0)(-1, 0) and (6,0) (6, 0).

Therefore, the solution to the problem is (1,0),(6,0)(-1, 0), (6, 0).

3

Final Answer

(1,0),(6,0) (-1,0),(6,0)

Key Points to Remember

Essential concepts to master this topic
  • Definition: X-intercepts occur where the graph crosses the x-axis (y = 0)
  • Technique: Factor x2+5x+6=(x+1)(x6)=0 -x^2 + 5x + 6 = -(x+1)(x-6) = 0
  • Check: Substitute x = -1 and x = 6: both give f(x) = 0 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting the negative sign when factoring
    Don't factor x2+5x+6 -x^2 + 5x + 6 as (x+1)(x6) (x+1)(x-6) = wrong expanded form! The negative coefficient of x² means you need (x+1)(x6) -(x+1)(x-6) or factor out -1 first. Always account for the leading negative coefficient.

Practice Quiz

Test your knowledge with interactive questions

The following function has been graphed below:

\( f(x)=-x^2+5x+6 \)

Calculate points A and B.

BBBAAACCC

FAQ

Everything you need to know about this question

Why are points A and B both on the x-axis?

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X-intercepts are where the parabola crosses the x-axis, so their y-coordinates are always zero. That's why we set f(x)=0 f(x) = 0 to find them!

How do I know which point is A and which is B from the graph?

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Look at the graph! Point A is on the left at (-1, 0) and point B is on the right at (6, 0). The labels match their positions on the coordinate plane.

Can I use the quadratic formula instead of factoring?

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Absolutely! The quadratic formula x=b±b24ac2a x = \frac{-b \pm \sqrt{b^2-4ac}}{2a} will give you the same answers: x = -1 and x = 6. Factoring is just faster when it works easily.

What if I can't factor the quadratic?

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If factoring seems difficult, try the quadratic formula or completing the square. Not all quadratics factor nicely with integers, but they all have solutions!

Why do we set the equation equal to zero?

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We want to find where the graph touches the x-axis, which means y = 0. Since y = f(x), we solve f(x)=0 f(x) = 0 to find these special x-values.

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