For a G.P.
i)
If t3 = 20, t6= 160, find S7.
ii) If t4 =16, t9=512, find S10.
Answers
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3
Answer:
Step-by-step explanation:
Let a and r and first term nad common ratio
Then t3=ar²=20
t6=ar^5=160
t6/t3=ar^5/ar^2=160/20
=r³=8
r=2
ar^2=20
a*4=20,a=5
So S7=a(r^7-1)/(r-1)
=5(2^7-1)/(2-1)
=5*(128-10=127*5=635
========================
ii) If t4 =16, t9=512, find S10.
t9/t4=ar^8/ar^3=r^5=512/16=32=25
r=2
r4=ar^3=16
a*8=16
a=2
s1o=a(r^10-1)/(r-1)
=2(2^10-1)/(2-1)
=2(1024-1)
=2*1023=2046
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