If a1,a2,a3...anare in AP and a1=0, then the value of a3a2+a4a3+….+anan-1-a21a2+1a2+....+1an-2 is equal to
Finding the value of (a3a2+a4a3+….+anan-1)-a2(1a2+1a2+....+1an-2):
Given that a1,a2,a3...an are in AP
and a1=0
a2=a1+d=da3=a1+2d=2dan-1=(n-2)dan=(n-1)da3a2+a4a3+….+anan-1-a21a2+1a2+....+1an-2
=2dd+3d2d+...(n-1)d(n-2)d-d1d+12d+...+1(n-3)d
=2+32+...(n-1)(n-2)-(1+12+...+1(n-3)) ={(1+1)+(1+12)+...(1+1(n-2)}-{1+12+13+...+1(n-3)}
=1+1+1+....(n-2) Terms
+{1+12+13+....+1(n-3)+1(n-2)}-{1+12+13+...+1(n-3)}=(n-2)+1(n-2)
Hence, the value is (n-2)+1(n-2).