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=8.7055056329612 a3=a2q=13.195079107729 a4=a3q=20 a5=a4q=30.314331330208 a6=a5q=45.947934199881 a7=a6q=69.64404506369 a8=a7q=105.56063286183 a9=a8q=160 a10=a9q=242.51465064166 a11=a10q=367.58347359905 a12=a11q=557.15236050952 a13=a12q=844.48506289465 a14=a13q=1280 a15=a14q=1940.1172051333 a16=a15q=2940.6677887924 a17=a16q=4457.2188840762 a18=a17q=6755.8805031572 a19=a18q=10240 a20=a19q=15520.937641066 a21=a20q=23525.342310339 a22=a21q=35657.751072609

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