a,ar,ar2....T2+T6=225⇒ar(1+r4)=225
a2r2(1+r4)2=4625⋯(1)
T3⋅T5=25⇒(ar2)(ar4)=25
a2r6=25...(2)
On dividing (1) by (2)
r4(1+r4)2=425
4r8−17r4+4=0
(4r4−1)(r4−4)=0
r4=41,4⇒r4=4 (an increasing geometric series)
a2r6=25⇒(ar3)2=25
T4+T6+T8=ar3+ar5+ar7
=ar3(1+r2+r4)
=5(1+2+4)=35