if in an A.P 3rd term is 18 and 17th term is 30. Sum of its 17 terms is:
(I'm not getting the right answer)

Question

if in an A.P 3rd term is 18 and 17th term is 30. Sum of its 17 terms is:
(I'm not getting the right answer)

diyadiya · Answer

3rd Term= a+2d
17thTerm=a+16d

experimentx · Answer

18 = a+2d; 30 =a+16d solve them, find a and d, use in formula of Sn to get value http://www.wolframalpha.com/input/?i=18+%3D+a%2B2d%3B+30+%3Da%2B16d

diyadiya · Answer

Ok so solution given in my book is wring :)

experimentx · Answer

http://www.wolframalpha.com/input/?i=17%2F2%282*114%2B16*6%2F7%29

callisto · Answer

3rd Term= a+2d =18  -(1)
17thTerm=a+16d =30  -(2)
(2)-(1)
14d = 12
d = 12/14 = 6/7
a + 2(6/7) =18 
a = 114/7

Sum = (114/7 + 30) x17 /2 = something ugly :S

experimentx · Answer

i think we should have a calculator applet

diyadiya · Answer

Yup! Something ugly 
But the answer given in the book was 612 
So its wrong =)

Thank you :)

anonymous · Answer

attachment

anonymous · Answer

... isn't that ugly ? LOL

diyadiya · Answer

Definitely :)