7 %2B 10 \frac 1 2 %2B 14 %2B \ldots %2B 84

1.	7 %2B 10 \frac 1 2 %2B 14 %2B \ldots %2B 84
Answer» a=7a2=10.5a3=14which is an ap sinch a2-a1=a3-a2* a=7 d = a2-à=3.5a.qAn=84a+(n-1)d=84putting values7+(n-1)3.5=84 a= 7l= an= 84d=a2−a1=– 7 = 21/2 – 7 = 7/2d= 7/2 Let 84 be thenthterm of this A.P.l=a(n– 1)d84 = 7+ (n– 1) × 7/277 = (n– 1) × 7/222 =n− 1n= 23 We know that,Sn=n/2 (a+l) Sn= 23/2(7 + 84) = (23×91/2) = 2093/2 Sn=1046 1/2

Answer»

a=7a2=10.5a3=14which is an ap sinch a2-a1=a3-a2* a=7 d = a2-à=3.5a.qAn=84a+(n-1)d=84putting values7+(n-1)3.5=84

a= 7l= an= 84d=a2−a1=– 7 = 21/2 – 7 = 7/2d= 7/2

Let 84 be thenthterm of this A.P.l=a(n– 1)d84 = 7+ (n– 1) × 7/277 = (n– 1) × 7/222 =n− 1n= 23

We know that,Sn=n/2 (a+l)

Sn= 23/2(7 + 84) = (23×91/2) = 2093/2

Sn=1046 1/2

Discussion