2 answers:
Answer:
PLS MARK BRAINLIEST
Step-by-step explanation:
Sn = n/2(2a+(n-1)d)
a=6
a+ 4d= 18
6 +4d= 18
4d = 12
d = 3
162= n/2(12+(n -1)3)
324=n(12 + 3n-3)
324=12n + 3n^2 - 3n
3n^2 + 9n-324=0
3n^2+ 36n-27n -324 =0
3n(n+12) -27(n+12)= 0
3n-27 =0; n+ 12=0
n=9 ; n= -12
since n can't be negative n=9
The number of terms is 9
Answer:
number of terms=9
Step-by-step explanation:
![t_{1}=6\\t_{5}=18\\\\t_{n}=t_{1}+(n-1)d\\18=6+(5-1)d\\18-6=4d\\4d=12\\d=12/4=3\\s_{n}=162\\s_{n}=\frac{n}{2}[2t_{1}+(n-1)d]\\162=\frac{n}{2}[2(6)+(n-1)3]\\162 \times 2=n(12+3n-3)\\324=n(3n+9)\\3n^2+9n-324=0\\n^2+3n-108=0\\n^2+12n-9n-108=0\\n(n+12)-9(n+12)=0\\(n+12)(n-9)=0\\n=-12,9\\n=-12 (rejected)](https://tex.z-dn.net/?f=t_%7B1%7D%3D6%5C%5Ct_%7B5%7D%3D18%5C%5C%5C%5Ct_%7Bn%7D%3Dt_%7B1%7D%2B%28n-1%29d%5C%5C18%3D6%2B%285-1%29d%5C%5C18-6%3D4d%5C%5C4d%3D12%5C%5Cd%3D12%2F4%3D3%5C%5Cs_%7Bn%7D%3D162%5C%5Cs_%7Bn%7D%3D%5Cfrac%7Bn%7D%7B2%7D%5B2t_%7B1%7D%2B%28n-1%29d%5D%5C%5C162%3D%5Cfrac%7Bn%7D%7B2%7D%5B2%286%29%2B%28n-1%293%5D%5C%5C162%20%5Ctimes%202%3Dn%2812%2B3n-3%29%5C%5C324%3Dn%283n%2B9%29%5C%5C3n%5E2%2B9n-324%3D0%5C%5Cn%5E2%2B3n-108%3D0%5C%5Cn%5E2%2B12n-9n-108%3D0%5C%5Cn%28n%2B12%29-9%28n%2B12%29%3D0%5C%5C%28n%2B12%29%28n-9%29%3D0%5C%5Cn%3D-12%2C9%5C%5Cn%3D-12%20%28rejected%29)
as number of terms can't be negative.
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