Explain why you think area calculations for polygons use different formulas?

Hello, i need compare km^2 and km. what's difference in this?

Use mathematical induction to prove the statement is true for all positive integers n, or show why it is false. 1^2 + 4^2 + 7^2 + + (3n - 2)^2 = [n(6n^2-3n-1)/2]

Find the measure of the missing angle