S20 = 20/2 (T1+T20)
d = (T12-T9)/3
T1 = T9-8d
Now just plug and chug.
pls help me out in dis ? dat says The 9th term of an Ap is 52 while d 12th term is 70 find d sum of it's 20th term?
3 answers
1220
1220