Question

Explain why 7 × 11 × 13 + 13 and 7 × 6 × 5 × 4 × 3 × 2 × 1 + 5 are composite numbers.

Answer 1

7×11×13+13 may be written as, 13x{(7x11) + 1} i.e. 13x(78). So other than 1 and the number itself, 13 and 78 are also the factors of the number. Further, 78=39x2. So, 39 and 2 are also it's factors. So this number is definitely not prime. Hence its composite number.

Answer 2

hey friend..!!
@_@

7 x 11 x13+13. and. 7 x6x45x4x3x2x1+5
=13 x(7 x11 +1) =5(7x6x4x3x2x1+1)
=13 x(77 +1) this is not a prime
=13 x 78. number.
13x78 cant be a
prime number because
it has a factor of 13.

therefore, they are composite number..

@_@
HOPE IT HELP U ..