X^2+15^2=25^2
X^2+225=625
Isolate X
X^2=400
Take the square root on both sides
X=positive and negative 20 but in this case the negative is thrown out because you can't have a negative side
Answer: 20
A, B, D are functions.
(First, second, and fourth response)
You can see which is function since for everyone input only has one value. You can also use the vertical line test.

<em>Golden ratio, also known as the golden section, golden mean, or divine proportion, in mathematics, the irrational number (1 + Square root of√5)/2, often denoted by the Greek letter ϕ or τ, which is approximately equal to 1.618.</em>
Answer:
C) 
Step-by-step explanation:
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Therefore, this solution is genuine.
I am joyous to assist you anytime.