how many terms of an arithmetic sequence 4,10,16... is added to give 310??
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Step-by-step explanation:
a=4
d=a2-a1
=10-4
d=6
s=310
n=?
Sn= n/2[ 2a+(n-1)d]
310=n/2[ 2×4+(n-1)6]
310×2=n[8+6n-6]
620=n[2+6n]
620=2n+6n^2
6n^2+2n-620=0
÷2
3n^2+n-310=0
3n^2+31n-30n-310=0
n(3n+31)-10(3n+31)=0
3n+31=0, n-10=0
3n=-31, n=10
n=-31/3, n=10
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