Math, asked by shashank12, 1 year ago

find the sum of 3+7+11+......25 terms

Answers

Answered by lohithanaidu

a=3,n=25,d=7-3=4
S₂₅=n/2(2a+(n-1)d)
S₂₅=25/2[2(3)+(25-1)4]
S₂₅=25/2(6+96)
S₂₅=25/2(102)
S₂₅=25(51)
S₂₅=1275.

lohithanaidu: :)

dikshaverma4you: But y hv u put the value of n= 25.... As it is an...

shashank12: yes n=25

dikshaverma4you: How

shashank12: nth term is 25 then n=25

dikshaverma4you: If nth term would be 100, that doesn't mean that there are 100 terms......... For ex-----. AP-- 5,10,15,20.........100,,, so here there will be 20 terms. Not 100...... Similarly in the ques. nth term is 25.... So with the formula of nth term we'll take out the value of n ( no. Of terms)

dikshaverma4you: Okay in the ques. Its 25 terms.... I thought 25 is an

dikshaverma4you: Sorry

shashank12: haha ok finally u realized

dikshaverma4you: Yeah

Answered by dikshaverma4you

Sn= n/2[ 2a+(n-1) d].......... Here a=3,,,,,, d= 7-3= 4..... and n= 25.... S25= 25/2[6+24×4]..................... S25= 25/2[6+ 96]............................. S25= 25/2[102]........ Now, 102 is cancelled fro. 2... 51 remains...... S25= 51×25............. S25= 1275

dikshaverma4you: Hey plzz mark it as best...

shashank12: but answer is 1275

dikshaverma4you: Yeah... I have edited it.... I wrote by mistake 100 instead of 102

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