Given a1,a2,a3,5,4,a6,a7,a8,a9 are in H.P.
⇒a+3d=15;a+4d=14
where, a,d are first term and common diference of corresponding AP.
⇒a=d=120
D=∣∣
∣∣a1a2a354a6a7a8a9∣∣
∣∣
=203∣∣
∣
∣
∣∣11213141516171819∣∣
∣
∣
∣∣
applying C2→C2−12C1 and C3→C3−13C1 gives
=203∣∣
∣
∣∣1001434011217356463∣∣
∣
∣∣
=203(340⋅463−112⋅356)
=203×115×224=5021
∴[Δ]=[5021]=2 where [.] is greatest integer function.