Find Domains: Analyzing y=-(x-3 1/12)² - 1/7 Function

Domain Analysis with Downward Parabolas

Find the positive and negative domains of the function below:

y=(x3112)217 y=-\left(x-3\frac{1}{12}\right)^2-\frac{1}{7}

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Find the positive and negative domains of the function below:

y=(x3112)217 y=-\left(x-3\frac{1}{12}\right)^2-\frac{1}{7}

2

Step-by-step solution

The given quadratic function is y=(x3112)217 y = -\left(x - 3\frac{1}{12}\right)^2 - \frac{1}{7} . We start by understanding that the shape of this parabola will open downwards due to the negative sign in front of the square term. To find the roots or x-intercepts, set y=0 y = 0 .

Rewriting the expression for clarity, we have:

0=(x3712)217 0 = -\left(x - \frac{37}{12}\right)^2 - \frac{1}{7}

We can solve this by isolating the squared term:

(x3712)2=17 \left(x - \frac{37}{12}\right)^2 = -\frac{1}{7}

Since a squared term cannot be negative, it illustrates that there are no real roots. This means the parabola does not cross the x-axis and remains entirely below it, due to the downward opening.

Therefore, the function is negative (y<0 y < 0 ) for all x-values. The positive domain is non-existent.

The solution tells us:

  • x<0: x < 0 : all x x
  • x>0: x > 0 : none

In terms of given choices: the correct choice is 3.

The solution to the problem is that the positive and negative domains are:

x<0: x < 0 : all x x

x>0: x > 0 : none

3

Final Answer

x<0: x < 0 : all x x

x>0: x > 0 : none

Key Points to Remember

Essential concepts to master this topic
  • Vertex Form: Function y=(xh)2+k y = -(x - h)^2 + k opens downward when coefficient is negative
  • Technique: Set y=0 y = 0 to find x-intercepts: (x3112)2=17 (x - 3\frac{1}{12})^2 = -\frac{1}{7}
  • Check: Since squared terms cannot equal negative values, no real roots exist ✓

Common Mistakes

Avoid these frequent errors
  • Confusing positive/negative domains with function signs
    Don't think positive domain means where x > 0 and negative domain means where x < 0! This confuses input values with output signs. The question asks where the function output y is positive or negative. Always check if y > 0 or y < 0 for all x-values.

Practice Quiz

Test your knowledge with interactive questions

The graph of the function below does not intersect the \( x \)-axis.

The parabola's vertex is marked A.

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

AAAX

FAQ

Everything you need to know about this question

What does 'positive domain' and 'negative domain' actually mean?

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Positive domain means where the function output y>0 y > 0 (above x-axis), and negative domain means where y<0 y < 0 (below x-axis). It's about the function values, not the x-coordinates!

Why can't a squared term equal a negative number?

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Any real number squared is always positive or zero. For example: 52=25 5^2 = 25 and (3)2=9 (-3)^2 = 9 . So (x3112)2=17 (x - 3\frac{1}{12})^2 = -\frac{1}{7} has no real solutions.

How do I know this parabola opens downward?

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Look at the coefficient of the squared term! Since we have y=(x3112)217 y = -(x - 3\frac{1}{12})^2 - \frac{1}{7} , the negative sign in front means it opens downward like an upside-down U.

If there are no x-intercepts, how do I find where it's positive or negative?

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Test any point! Since the parabola opens downward and never crosses the x-axis, it's entirely below the x-axis. This means y<0 y < 0 for all x-values, so the negative domain is all real numbers.

Why does the answer say 'x < 0: all x' instead of 'all real numbers'?

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The question asks specifically about negative x-values (x < 0) and positive x-values (x > 0). Since the function is negative everywhere, it's negative for all x < 0 and also negative for all x > 0.

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