Geometric sequence

In the geometric sequence is a4 = 20 a9 = -160. Calculate the first member a1 and quotient q.

Correct answer:

q =  -1.5157
a1 =  -5.7435

Step-by-step explanation:

a9=a1q8=160 a4=a1q3=20  16020=q8q3  8=q5 (8)0.2=q q=1.5157
a9=a1q8 a1=160q8=5.7435 a2=a1q=8.70550563296 a3=a2q=13.1950791077 a4=a3q=20 a5=a4q=30.3143313302 a6=a5q=45.9479341999 a7=a6q=69.6440450637 a8=a7q=105.560632862 a9=a8q=160 a10=a9q=242.514650642 a11=a10q=367.583473599 a12=a11q=557.15236051 a13=a12q=844.485062895 a14=a13q=1280 a15=a14q=1940.11720513 a16=a15q=2940.66778879 a17=a16q=4457.21888408 a18=a17q=6755.88050316 a19=a18q=10240 a20=a19q=15520.9376411 a21=a20q=23525.3423103 a22=a21q=35657.7510726

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