Question

the sum of the first twelve terms of an arithmetic progression is 21 and the sum of the first 21 terms of the same arithmetic progression is 12 then find the 17th term of the arithmetic progression

Answer 1

S(12)=21
21=6(2a+5d)
21=12a+30d

S(21)=12
12=21/2(2a+20d)
24=42a+420d

solving both equation we will find the value of a and d.
T(17)=a+16d
put the value of a and d u will find the answer