Watch the Sus-pender online guitar lesson by Brad Carlton from Chord Studies: Open String Chords Vol. 2
Here we are in the key of A playing a I-IV progression, but we are using inversions to climb up to the IV chord. We start off with an Asus2, fingering it with fingers 1 and 2. Your first finger will be a pivot as we go into the Asus2/C♯, which could be thought of enharmonically as an Aadd9. When switching to the Dadd9 make sure you don't disturb the first string, and let the second string ring for as long as possible.