Solve f(x) = x²: Finding the Missing Value When f(x) = 16

Quadratic Functions with Inverse Operations

Complete:

The missing value of the function point:

f(x)=x2 f(x)=x^2

f(?)=16 f(?)=16

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Set up and solve
00:04 We'll substitute appropriate values according to the given data, and solve for X
00:11 Extract the root
00:15 When extracting a root there are 2 solutions, positive and negative
00:22 These are the 2 points
00:27 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

Complete:

The missing value of the function point:

f(x)=x2 f(x)=x^2

f(?)=16 f(?)=16

2

Step-by-step solution

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

  • Step 1: Set up the equation from the function definition.
  • Step 2: Solve the equation by taking the square root of both sides.
  • Step 3: Identify all possible values for x x .
  • Step 4: Compare with the given answer choices.

Now, let's work through each step:

Step 1: We start with the equation given by the function f(x)=x2 f(x) = x^2 . We know f(?)=16 f(?) = 16 , so we can write:

x2=16 x^2 = 16

Step 2: To solve for x x , we take the square root of both sides of the equation:

x=±16 x = \pm \sqrt{16}

Step 3: Solve for 16 \sqrt{16} :

The square root of 16 is 4, so:

x=4 x = 4 or x=4 x = -4

This gives us the two solutions: x=4 x = 4 and x=4 x = -4 .

Step 4: Compare these solutions to the answer choices. The correct choice is:

f(4) f(4) and f(4) f(-4)

Therefore, the solution to the problem is f(4) f(4) and f(4) f(-4) .

3

Final Answer

f(4) f(4) f(4) f(-4)

Key Points to Remember

Essential concepts to master this topic
  • Setup: Set function equal to given value: x² = 16
  • Technique: Take square root of both sides: x = ±√16 = ±4
  • Check: Verify both solutions: f(4) = 4² = 16 and f(-4) = (-4)² = 16 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting the negative solution when taking square roots
    Don't just write x = 4 when solving x² = 16 = only half the answer! This misses the fact that both positive and negative numbers square to give positive results. Always write x = ±√16 to get both x = 4 and x = -4.

Practice Quiz

Test your knowledge with interactive questions

Complete:

The missing value of the function point:

\( f(x)=x^2 \)

\( f(?)=16 \)

FAQ

Everything you need to know about this question

Why are there two answers when solving x² = 16?

+

Because both positive and negative numbers give the same result when squared! Think about it: 42=16 4^2 = 16 and (4)2=16 (-4)^2 = 16 . That's why we always need the ± symbol.

How do I know which answer choices to pick?

+

Look for the choice that includes both solutions! Since we found x = 4 and x = -4, we need f(4) f(4) and f(4) f(-4) together.

What if I only wrote x = 4 as my answer?

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You'd be half right but missing a solution! Quadratic equations usually have two solutions, so always check for both positive and negative roots.

How can I check my work?

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Substitute both values back into the original function:

  • f(4)=42=16 f(4) = 4^2 = 16
  • f(4)=(4)2=16 f(-4) = (-4)^2 = 16
If both give you 16, you're correct!

Is this the same as solving any equation with x²?

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Yes! Whenever you see x2=positive number x^2 = \text{positive number} , take the square root of both sides and don't forget the ± symbol for both solutions.

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