Question

K= n times n + 9n +1

Mo says;
" K will be a prime number for all integer values of 'n' from 1 to 9"

Show that Mo is wrong.
You must show that your value "K" is NOT prime.

Answer 1

k = n(n^2 +9n+1)

expand brackets

k = n^3 + 9n^2 + n

first subsitute 1 as n to see if the result is prime.

k = (1)^3 + 9(1)^2 + 1

k = 1 + 9 + 1

k = 11 (this number is prime)

then substitute 2

k = (2)^3 + 9 (2)^2 + 2

k = 8 + 9 (4) + 2

k = 36 + 10

k = 46 (THIS NUMBER IS NOT PRIME SO MO IS WRONG)