Multiply through the parentheses:
-24 + 18i + 8i + 6
18 + 26i
18 + 26i is the answer
A^2 + b^2 = c^2
9^2 + b^2 = 15^2
81 + b^2 = 225
225 - 81 = b^2
144 = b^2
square root of 144 = 12
b = 12

In this case the 5 is on top so it is the Numerator
Given the arithmetic sequence is given by:
an=4-3(n-1)
writing the above into a straight line form we get:
an=4+3-3n
an=-3n+4
this a straight line equation with a negative slope, thus the domain will be:
(-∞,∞)
See attached picture for the answer: