The 3rd and 6th terms of a G. P are 108 and -32 respectively. Find the sum of the first 7 terms
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Hey buddy... here's your answer
3rd term=a3=108=a+2d
6th term=a6= -32=a+5d
S7= sum of first 7 terms=?
a+2d=108
(-)a+(-)5d=(+)-32
-----------------------------------
-4d=140
d=-35
a+2d=108
a+2(-35)=108
a-70=108
a=108+70
a=178
a7=a+6d
=178+6(-35)
=178-210
=-22
S7=n/2(a+a7)
=7/2(178-22)
=7/2(156)
=7(78)
=546
The sum of first 7 terms is 546.
I hope this will be helpful
3rd term=a3=108=a+2d
6th term=a6= -32=a+5d
S7= sum of first 7 terms=?
a+2d=108
(-)a+(-)5d=(+)-32
-----------------------------------
-4d=140
d=-35
a+2d=108
a+2(-35)=108
a-70=108
a=108+70
a=178
a7=a+6d
=178+6(-35)
=178-210
=-22
S7=n/2(a+a7)
=7/2(178-22)
=7/2(156)
=7(78)
=546
The sum of first 7 terms is 546.
I hope this will be helpful
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