Question

If m=( -28)+26+(-28)+36+_(40 terms)

Answer 1

take (-28) as common for all terms

we get.

-28×(36+46+56+....upto 40 terms)

taking sum of the 40 terms by the equation.

S =n/2×[2a+{(n-1)×d}]

a=36

n=40

and. d=10.

so.

S =40/2×[2×36+{(40-1)×10}].

we get

20×[72+{36×10}]

which is equal to

20×[72+360]

=20×432

=8640

now multiply this value with -28.

then we get.

-28×8640.

= -241920.