IB AA HL May 2026 P1 TZA Q3

Consider a geometric sequence, \(u_n\), with common ratio \(r\), where each term in the sequence is positive. It is given that \(u_6=1.6\times10^5\) and \(u_8=6.4\times10^5\).

1. Find the value of \(r\).[3]
2. Find the value of \(u_1\), giving your answer in the form \(a\times10^k\), where \(1\leq a<10\) and \(k\in\mathbb{Z}\).[3]