NCERT Solutions For Class 11 Math Chapter – 7 Exercise – 7.2

NCERT Solutions For Class 11 Math Chapter – 7 Exercise – 7.2

 

Q1.  Evaluate

  • 8!
  • 4! – 3!

Solution:-

 

  • 8! = 1 x 2 x 3 x 4 5 x 6 x 7 x 8 = 40320
  • 4! = 1 x 2 x 3 x 4 = 24

3! = 1 x 2 x 3 = 6

4! – 3! = 24 – 6 = 18

 

Q2. Is 4! + 3! = 7! ?

Solution:-

 

3! = 1 x 2 x 3 = 6

4! = 1 x 2 x 3 x 4 = 24

Therefore,

3! + 4! = 6 + 24 = 30

7! = 1 x 2 x 3 x 4 x 5 x 6 x7 = 5040

 

Hence

3! + 4!   ≠ 7!

 

Q3.  Compute 8!/6! x 2!

Solution:-

 

8!/6! x 2! = 8×7/2 = 28

 

Q4. If 1/6! + 1/7! = x/8! find x.

Solution:-

 

1/6! + 1/7! = x/8!

1/6! + 1/7! = x/8 x 7 x 6!

1/6! (1+1/7) = x/8 x 7 x 6!

X = 64

 

Q5. Evaluate n!/(n-r)! when

  • n = 6 r = 2  
  • N = 9 , r = 5

Solution:-

 

  • N!/(n-r)! = 6!/(6-2)!

= 6!/5!

= 6 x 5 x 4!/4!

= 30

 

  • When n = 9 r = 5!

N!/(n-r)! = 9!/(9-5)!

= 9!/4!

= 9 x 8 x 7 x 6 x 5 x 4!/4!

= 15120