Question 1 and 2, Exercise 4.3
Solutions of Question 1 and 2 of Exercise 4.3 of Unit 04: Sequence and Series. This is unit of Model Textbook of Mathematics for Class XI published by National Book Foundation (NBF) as Federal Textbook Board, Islamabad, Pakistan.
Question 1
Find the sum of series: 4+7+10+13+16+19+22+25
Solution. Given: 4+7+10+13+16+19+22+25.
As the given series is arithmetic series with a1=4, d=7−4=3, n=8, so
Sn=n2[2a1+(n−1)d]⟹S8=82[2(4)+(8−1)(3)]=4[8+7×3]=116
Hence sum of given series is 116.
Question 2
Find the sum of series. a1=2, an=200, n=100
Statement is logically incorrenct.
Find the sum of arithematic series with: a1=2, an=200, n=100
Solution.
Given a1=2, an=200, n=100.
Let Sn represents sum of arithematic series. Then
Sn=n2[a1+an]⟹S100=1002[2+200]=10100.
Hence S100=10100.
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