Question

a=-6 and d= 2 . find its first 20 terms .​

Answer 1

$\huge \fbox \purple{❥ Answer}$

Let a be the first term and d be the common difference of the given A.P. 

Then,  a3=7 and a7=3a3+2

⟹a+2d=7 and a+6d=3(a+2d)+2

⟹a+2d=7 and a+6d=3(a+2d)+2

⟹a+2d=7 and a=−1

⟹a=−1 and d=4

Putting n=20,a=−1 and d=4 in Sn=2n{2a+(n−1)d}, we get

S20=220{2×−1+(20−1)×4}=220(−2+76)=740

Answer 2

QUESTION⤵️

a=-6 and d= 2 . find its first 20 terms .

ANSWER⤵️

second term= a2

a2= a+d

= -6+2

a2= -4

a3= a+2d

= -6+4

a3= -2

a4= a+3d

=-6+6

a4=0

a5= a+4d

= -6+8

a5= 2

a6= a+5d

= -6+10

a6= 4

a7= a+6d

= -6+12

a7= 6

IN THIS WAY WE WILL FIND UPTO 20 TERMS....

-6,-4,-2,0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30

HOPE IT HELPS