the sum of 7th and 3rd term in a.P is 6 their product is 8 .find the sum of the first 20 terms of the a.p
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Answered by
6
a7+a3=6
a+6d+a+2d=6
2a+8d=6_______(1)
2(a+4d)=6
a+4d=3_______
product is 8
(a+6d)(a+2d)=8
3+2d)(3-2d)=8
9-4d^2 = 8
d=1/2
sub in 1
a+4(1/2)=3
a+2=3
a=1
s20=20/2(2(1)+19(1/2))
=10(2+19/2)
=10(4+19)/2
=5(23)
=115
a+6d+a+2d=6
2a+8d=6_______(1)
2(a+4d)=6
a+4d=3_______
product is 8
(a+6d)(a+2d)=8
3+2d)(3-2d)=8
9-4d^2 = 8
d=1/2
sub in 1
a+4(1/2)=3
a+2=3
a=1
s20=20/2(2(1)+19(1/2))
=10(2+19/2)
=10(4+19)/2
=5(23)
=115
Answered by
3
it is easy we have to know some basic trick to solve it
I have solved it which I gave attachments
I have solved it which I gave attachments
Attachments:
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