hilarypatricks
Answered

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Very urgent!!!!!
The first term of an AP is 6 and the 5th term is 18.find the number of terms in the series having a sum of 162....
With workings
And explanation
Thanks ​

Sagot :

Answer:

number of terms=9

Step-by-step explanation:

[tex]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)[/tex]

as number of terms can't be negative.

crissz67

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

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