ANSWER
The radius is 4
EXPLANATION
The given equation is:

We complete the square to get the expression in standard form:


We factor using perfect squares to get:

This implies that,

Comparing to

The radius is r=4
C a rectangle. brainily says this is too short so I am writing more
Answer:
The answer is the last one: One runner in the study runs 31...
Step-by-step explanation:
31 is the input (x) and 81 is the output (y) and since there's 1 ordered pair per runner, it's going to be one runner, and the input is the miles ran.

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Answer:
-90
Step-by-step explanation: