the first term of a G.P. is 1. the sum of third and fifth terms is 90. find the common ratio of the G.P.
Answers
Answered by
18
a1= 1
a3 + a5 = 90
a3= a1*r^2 = r^2
a5 = a1 *r^4 = r^4
=r^2 + r^4 = 90
= r^4 + r^2 - 90 =0
= (r^2 + 10) (r^2 - 9) = 0
= (r^2 + 10) ( r-3)(r+3) = 0
r=+3,-3
Answered by
11
Hi there!
, , , ..... is a Geoometric progression.
Given,
= 1
+ = 90
But_
= r² = r²
= r⁴ = r⁴
r² + r⁴ = 90
r⁴ + r⁴ - 90 = 0
(r2 + 10) (r² - 9) = 0
(r² + 10) ( r - 3)(r + 3) = 0
Thus,
= 3
= -3
Hope it helps! :D
Cheers,
Ishaan Singh
, , , ..... is a Geoometric progression.
Given,
= 1
+ = 90
But_
= r² = r²
= r⁴ = r⁴
r² + r⁴ = 90
r⁴ + r⁴ - 90 = 0
(r2 + 10) (r² - 9) = 0
(r² + 10) ( r - 3)(r + 3) = 0
Thus,
= 3
= -3
Hope it helps! :D
Cheers,
Ishaan Singh
Anonymous:
wrong and copied
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