Asked by Vijay

If for a g.p. S2=8 and s4=80,find its first term and the common ratio.
Answered by Bosnian
s2 = s1 * q

s4 = s1 * q ^ 3


8 = s1 * q


40 = s1 * q ^ 3


s1 * q ^ 3 = s1 * q * q ^ 2


40 = s1 * q ^ 3 = ( s1 * q ) * q ^ 2 = 8 * q ^ 2

40 = 8 * q ^ 2

40 / 8 = q ^ 2

5 = q ^ 2

q = ± sqrt ( 5 )


You can construct two g.p.

1.

8 = s1 * g

8 = s1 / sqrt ( 5 )

s1 = 8 / sqrt ( 5 )


2.

8 = s1 * g

8 = s1 / - sqrt ( 5 )

s1 = - 8 / sqrt ( 5 )

















Answered by Rio
Sir answer a=2,r=3,
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