Answers

2016-02-18T19:30:50+05:30
A4/a9 = 1/3

a+3d/a+8d = 1/3

(a+3d)3 = (a+8d)
3a+9d = a+8d
2a+d = 0
d = -2a

a12/a5

a+11d/a+4d

=a+11*(-2a)/a+4*(-2a)

=a-22a/a-8a

= -21a/-7a

=21/7

=3/1

=3:1

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2016-02-19T00:38:40+05:30
Given that ratio is 1:3.

That means, a9 = 3*a4.
Need to find, a12/a5.

a9=a+8d
a4=a+3d

a+8d=3a+9d
d=-2a

a12=a+11d=-21a
a5=a+4d=-7a
So ratio of a12 to a5 = -21a:-7a or 3:1//
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