Question

explain why 7*11*13+13 is a composite number

Answer 1

13 is common
13(7*11*1+1)
13*78
product of primes is composite num

Answer 2

(7 × 11 × 13) + 13
Can be written as

13[(7 × 11) + 1]
Or
13 × (77 + 1)
= 13 × 78

According,to the defination of composite numbers, they can be written as a product of any two numbers except one and itself.

So, the given expression is a composite number!