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20 The nth term of an arithmetic series is Un where un > 0 for all n.
The sum to n terms of the series is Sn
Given that u4 = 6 and that S11 = (u6)2 + 18
Find the value of u20

Respuesta :

caylus

Answer:

Hi,

[tex]u_{20}=30[/tex]

Step-by-step explanation:

[tex]u_n=u_1+(n-1)*r, \ r= commun\ ratio.\\u_4=u_1+3*r=6\\u_6=u_1+5r\\(u_6)^2=u_1^2+10ru_1+25r^2\\s_n=u_1+u_1+r+u_1+2r+...+u_1+10r=11*u_1+55r\\s_{11}=(u_6)^2+18\ \\\Longrightarrow\ u_1^2+10ru_1+25r^2+18=11u_1+55r\\\Longrightarrow\ 4r^2+2r-12=0\\\Longrightarrow\ 2r^2+r-6=0\\r=\dfrac{3}{2} \ or\ r=-2\ (excluded)\\\\u_1=6-3r=\dfrac{3}{2} \\\\\\\boxed{u_{20}=u_1+19*r=30}\\[/tex]

shubhamchouhanvrVT

The value of the 20th term of the arithmetic series will be 30

What is arithmetic progression?

An arithmetic progression or arithmetic sequence is a sequence of numbers such that the difference between the consecutive terms is constant.

Un  =  u₁+(n-1) x r

u₄  =  u₁  +(3 x r)=6

u₆ = u₁ +5r

u₆²=u₁²+10ru₁+25r²+18=11u₁+55r

Sn= u₁+u₁+r+u₁+2r+.............u₁+10r= (11 x u₁) +55 r

4r²+2r-12=0

2r²+r-6=0

r=3/2

u₁=6-3r=3/2

u₂₀=u₁+(19 x r)= 30

Hence the value of the 20th term of the arithmetic series will be 30

To know more about arithmetic progression follow

https://brainly.com/question/6561461

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