will this do schooly:
i) DRA = 90, DSA = 90 so DRAS is a cyclic quad.
Then DSR and DAR are angles standing on the same chord.
DSR = DAR
ii) DSC = DTC = 90, and since DSC and DTC stand on DC, DSTC is a cyclic quad.
That is, DST + DCT = 180
DST = 180 = DCT
iii) RST = DSR +...