Question

(i) Find the value of (-1.2)3

Answer 1

Answer:

General term is T

r

=r(r+1)(r+2)=r(r

2

+3r+2)=r

3

+3r

2

+2r

Hence required sum is =

r=1

∑

n

(r

3

+3r

2

+2r)

=

4

n

2

(n+1)

2

+3⋅

6

n(n+1)(2n+1)

+2⋅

2

n(n+1)

=

4

n

2

(n+1)

2

+

2

n(n+1)(2n+1)

+2⋅

2

n(n+1)

=

4

1

n(n+1)[n(n+1)+2(2n+1)+4]=

4

1

n(n+1)(n

2

+5n+6)=

4

1

n(n+1)(n+2)(n+3)

Answer 2

Answer:

(1.2)*3

1.2×1.2×1.2

1.2×1.2×1.2