You are right. In circle equation we have =r² so the correct answer will be C od D. But we have to calculate the center of a circle.

Complete the square:

And we have:

So the answer is C (the same left side of equation).
Given the equation:

You know that a lab technician finds that a sample of fluid has this pH:

Then, in order to find the hydrogen ion concentration of the fluid, you need to follow these steps:
1. Substitute the pH given in the exercise into the equation:

Multiply both sides by -1:

2. Solve for:

Remember that, by definition:

In this case, you can identify that:

Hence, substituting values and simplifying, you get:

Therefore, the answer is:
Answer: 28 in.
Step-by-step explanation:
The perimeter is the total distance around the entire figure. Because all the lengths of the sides are already given, you just have to add them all up.
P = 4 in. + 8 in. + 8 in. + 4 in. + 4 in. = 28 in.
The answer is 7 because it’s an equation