Question

in an ap of the first term is 2 the sum of first 5 terms is one fourth of the sum of next 5 terms find the sum of first 20 terms​

Answer 1

Answer:

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Step-by-step explanation:

Answer 2

$S_{1-5} =\frac{1}{4}S_{5-10}$

[a+(a+d)+(a+2d)+(a+3d)+(a+4d)] = 1/4 [ (a+5d)+(a+6d)+(a+7d)+

(a+8d)+(a+9d)]

(5a+10d) = 1/4 (5a+35d)

(a+2d) = 1/4 (a+7d)

4a+8d = a+7d

d = -3a = -3×2 = -6

$S_{20}$= (20/2) [2a + (20-1)d]

= 10 [(2×2) + (19×-6)]

=10(4 - 144)

= -1400