explain why 7*11*13+13 and 7*6*5*4*3*2*1+5 are composite number

Asked by FEHMEEDAH NAZNEEN | 7th Jul, 2010, 12:00: AM

Expert Answer:

Dear Student,
Let us represent the first number as X.
Then X = 7 x 11 x 13 + 13
Composite number is a number which has positive divisors other than one and itself.
Now,
X can be written as:
X = ( 7 x 11 + 1) x 13        ..( taking 13 as common)
   =  78 x 13
Hence we can represent X as a product of two divisors greater than one.
therefore, X is a composite Number.
Now similarly the other number can be written as:
Y = 7 x 6 x 5 x 4x 3x 2x 1 + 5
   = ( 7 x 6 x 4 x 3x 2 x 1 + 1 ) x 5
   = 1009 x 5
Hence Both are composite numbers.
Regards,
Topperlearning

Answered by  | 14th Jul, 2010, 09:46: AM

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