A book costs $13 correct to the nearest dollar.
Patrick has $ 120 correct to the nearest
10 dollars.
Find the maximum number of books
Patrick can buy.

9 (Patrick still have 3 dollars)

Step-by-step explanation:

Divide 120 by 13

(n^3 - n)

= n(n-1)(n+1)

since it is divisible by 3 and 2 ,because it is a multiple 3 consecutive number

if, n-1 is odd then n+1 is also odd, then it is a multiple of 9

but if, n-1 is even then n+1 is also even, then it is a multiple of 4

so, largest multiple = max(9*2, 4*3) = max(18, 12) = 18

(5x-1)^2= (5x)^2-2(5x)×1+(1)^2=25x^2-10x+1