Answer:
3
Explanation:
18,15,12,..........
S
n
=45=
2
[2a+(n−1)d]
=>
[2×18+(n−1)(−3)]=45
[36−3n+3]=45
=>n(39−3n)−90=0
=>39n−3n
−90=0
=>3n
−39n+90=0
=>n
−13n+30=0
−10n−3n+30=0
=>n(n−10)−3(n−10)=0
=>(n−10)(n−3)=0
=>n=10 or n=3
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