Question

what is the answer? please reply

Answer 1

Answer

first term =a1 =a+d

17 term =a17=a+16d

CASE 1 (SUM)

a+d+a+16d=40

2a+17d=40--------------------------1

CASE 2(sum)

a1=a+d

18 term=a18=a+17d

a+d+a+17d=43

2a+18d=43--------------------------2

[solve 1 and 2}

2a+17d=40

(-)2a+(-)18d=(-)43

17d-18d=40-43

-d=-3

d=3

substitute d=3 in equation 1

2a+17(3)=40

2a+51=40

2a= -11

                        a=-11/2

a) common difference=3

b) sum of 7 and 11 term = a7+a11

a+6d+a+10d

-11/2+6(3)+-11/2+10(3)

-11/2+18+-11/2+30

-11/2+36/2+-11/2+60/2

25/2+49/2

74/2=37

c) 9 term =a9=a+8d

-11/2+24

-11/2+48/2

=27/2