Write the first five terms of the geometric sequence. \[ a_{n}=2 a_{n-1}, a_{1}=20 \]

Step 1 ：The given sequence is a geometric sequence where each term is twice the previous term. The first term is given as 20. To find the next terms, we simply multiply the previous term by 2.

Step 2 ：Using the formula \(a_{n}=2 a_{n-1}\), we can calculate the first five terms of the sequence.

Step 3 ：The first term \(a_{1}\) is 20.

Step 4 ：The second term \(a_{2}\) is \(2 * a_{1}\) = 40.

Step 5 ：The third term \(a_{3}\) is \(2 * a_{2}\) = 80.

Step 6 ：The fourth term \(a_{4}\) is \(2 * a_{3}\) = 160.

Step 7 ：The fifth term \(a_{5}\) is \(2 * a_{4}\) = 320.

Step 8 ：Final Answer: The first five terms of the geometric sequence are \(\boxed{20, 40, 80, 160, 320}\).