# Ex 5.3, 2

Last updated at Dec. 8, 2016 by Teachoo

Last updated at Dec. 8, 2016 by Teachoo

Transcript

Ex 5.3 ,2 Find the sums given below (i) 7 + 101/2 + 14 + ………… + 84 7 + 10 1/2+14+…84 Here, a = 7 d = 10 1/2−7 = 21/2−7 = (21 − 14)/2 = 7/2 Also, last term = 𝑙 = 84 So, we use the formula S = 𝑛/2 (𝑎+𝑙) Putting values S = 23/2(7+84) S = 23/2×91 S = 2093/2 S = 1046.5 Ex 5.3 ,2 Find the sums given below (ii)34 + 32 + 30 + ……….. + 10 34 + 32 + 30 + … 10 Here, a = 34 d = 32 – 34 = –2 Also, last term = 𝑙 = 84 So, we use the formula S = 𝑛/2 (𝑎+𝑙) Putting values S13 = 13/2 (34+10) S13 = 13/2 (44) S13 = 286 Ex 5.3 ,2 Find the sums given below (iii) − 5 + (− 8) + (− 11) + ………… + (− 230) − 5 + (− 8) + (− 11) + ………… + (− 230) Here, a = –5 d = –8 – (–5) = –8 + 5 = –3 Also, last term = 𝑙 = –230 So, we use the formula S = 𝑛/2 (𝑎+𝑙) Putting values Sn = 76/2 (− 5+(−230)) Sn = 38 ( – 235) Sn = – 8930

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Davneet Singh

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