Question

algebric form of this sequence
The algebric form of an arithmetic sequence is 2n + 3.
a) What is its first term?
b) Whatn is the 20 th term of this sequence ?
c) Calculate the sum of first 20 terms of this sequence ?
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Answer 1

Answer:

(i) let the first term be 1 that is n=1

2n+3=2(1)+3=2+3=5=a1

Now take n=2 to find d

2n+3=2(2)+3=7=a2

(ii) 20th term of this sequence.

2n+3=2(20)+3=40+3=43

(iii) S20=? A=5 d=a2-a1=7-5=2 n=20

S20=n/2(2a+(n-1)d

S20= 20/2(2(5)+(20-1)2)

S20=10(10+38)

S20=10(48)

S20=480

Sum of first 20 terms is 480

Thank you