Someone pls help me I don’t understand it at all

D. 4 root 113

Step-by-step explanation:

we have to use Pythagorean Theorem which is

a^2 + b^2 = c^2

where a and b are legs of the triangle that are 45° apart and c is the hypotenuse.

now we just plug in our values.

a^2 + (9)^2 = (47)^2

a^2 + 81 = 2209

now we're gonna solve for A (the missing side)

a^2 = 2128

now we square root both sides to undo the square on A

root(a^2) = root(2128)

because 2128 isn't a pretty root, we have to simplify it

a = 4 root(133)

Step-by-step explanation: