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.

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=74=3, n=8, so Sn=n2[2a1+(n1)d]S8=82[2(4)+(81)(3)]=4[8+7×3]=116 Hence sum of given series is 116. GOOD

Find the sum of series. a1=2, an=200, n=100

FIXME 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.