We know that:

Substituting known values, we have:

Answer:
x = ±20
Step-by-step explanation:
Step 1: Write equation
x² = 400
Step 2: Square root both sides
x = ±√400
x = ±20
Step 3: Check
<em>Plug in x to verify it's a solution.</em>
20² = 400
400 = 400
(-20)² = 400
400 = 400
Answer:
W ≈ 5.2 cm
Step-by-step explanation:
Represent the length and width by L and W respectively.
Then L * W = 81 cm^2, and L = 3W.
Substituting 3W for L in the first equation, we get:
3W * W - 81 = 0, or 3W^2 - 81 = 0.
To make it easier to find the final answer, rewrite 3W^2 - 81 = 0 as
81
W^2 = ------- = 27
3
Then W (the width) is the positive square root of 27, or W ≈ 5.2 cm
<u>Given:</u>
The given function is 
We need to determine the reflection of f(x) over the x - axis
<u>Reflection over x - axis:</u>
The translation rule to reflect over the x - axis is given by

Thus, applying the rule, the function becomes

Multiplying both sides of the equation by -1, we have;

This can be written as

Hence, the reflection of the function over the x - axis is 
Thus, Option A is the correct answer.