The formula for the nth term of a geometric sequence:
\(a_n=a_1 \times r^{n-1}\)
a₁ - the first term, r - the common ratio
\(54, a_2, a_3, 128 \\ \\
a_1=54 \\
a_4=128 \\ \\
a_n=a_1 \times r^{n-1} \\
a_4=a_1 \times r^3 \\
128=54 \times r^3 \\
\frac{128}{54}=r^3 \\ \frac{128 \div 2}{54 \div 2}=r^3 \\
\frac{64}{27}=r^3 \\
\sqrt[3]{\frac{64}{27}}=\sqrt[3]{r^3} \\
\frac{\sqrt[3]{64}}{\sqrt[3]{27}}=r \\
r=\frac{4}{3}\)
\(a_2=a_1 \times r= 54 \times \frac{4}{3}=18 \times 4=72 \\
a_3=a_2 \times r=72 \times \frac{4}{3}=24 \times 4=96 \\ \\
\boxed{a_2=72, a_3=96}\)
