Best U2 Music Videos

Source:@U2 Podcast, edition 3-1

BOSTON - Tom Petty and the Heartbreakers rocked a sold-out Garden to the rafters Friday night without a whiff of U2’s pomp, Stonesian swagger, or the Red Hot Chili Peppers’ raw energy - just first-class, meat-and-potatoes anthems from one of the finest live bands in America.

Source:Petty rocks Garden with his hit list (Worcester Telegram & Gazette)

Given that:

Arithmetic Progression:
U1=a ,
U2=a+d ,
U3=a+2d ,
U4=a+3d ,
…
Un=a+(n-1)d

and Un=[ Un-1 + Un+1 ] / 2

Geometric Progression:
U1=a ,
U2=ar ,
U3=ar^2 ,
U4=ar^3 ,
…
Un=ar^(n-1)

and Un=sqrt[ Un-1 x Un+1 ]

Arithmetic-Geometric Progression:
U1=a ,
U2=(a+d)r ,
U3=(a+2d)r^2 ,
U4=(a+3d)r^3 ,
…
Un=[ a+(n-1)d ] r^(n-1)

and Un=[ r Un-1 + Un+1 / r ] / 2

My question is is there a formula for obtaining Un (for an AGP) by just using Un-1 and Un+1 without having to find r , or is it impossible ?

Thanks.

Source:Open Question: Maths Question about Arithmetic-Geometric Progressions…?

Bono composed this song to his father

Original U2 Video