Please wait...
Contact Us
Contact
Need assistance? Contact us on below numbers

For Study plan details

93219 24448 / 89292 63204

10:00 AM to 7:00 PM IST all days.

For Franchisee Enquiry

81783 72169
OR

Chat with us on WhatsApp

or

Thanks, You will receive a call shortly.
Customer Support

You are very important to us

For any content/service related issues please contact on this number

93219 24448 / 99871 78554

Mon to Sat - 10 AM to 7 PM

Home / Doubts and Solutions/KERALA/Class 11 Science/Mathematics

If the sum of a certain no. of terms of the A.P. 25,22,19,...is 116.Find the last term.

Asked by mythili Suresh 2nd September 2015, 8:14 PM
Answered by Expert
Answer:
G i v e n space A P space i s space 25 comma 22 comma 19 comma... I n i t i a l space t e r m comma space a equals 25 C o m m o n space d i f f e r e n c e comma space d equals 22 minus 25 equals negative 3 A l s o space g i v e n space t h a t space t h e space s u m space o f space n space t e r m s space i s space 116 W e space k n o w space t h a t comma S subscript n equals n over 2 open square brackets 2 a plus open parentheses n minus 1 close parentheses d close square brackets comma space w h e r e space i s space t h e space n u m b e r space o f space t e r m s comma space a space i s space t h e space i n i t i a l space t e r m comma space S subscript n space i s space t h e space s u m space o f space n space t e r m s space a n d space l space i s space t h e space l a s t space t e r m. T h u s comma space w e space h a v e comma 116 equals n over 2 open square brackets 2 cross times 25 plus open parentheses n minus 1 close parentheses open parentheses negative 3 close parentheses close square brackets rightwards double arrow 232 equals n open square brackets 50 minus 3 open parentheses n minus 1 close parentheses close square brackets rightwards double arrow 232 equals 50 n minus 3 n open parentheses n minus 1 close parentheses rightwards double arrow 232 equals 50 n minus 3 n squared plus 3 n rightwards double arrow 3 n squared minus 53 n plus 232 equals 0 rightwards double arrow 3 n squared minus 24 n minus 29 n plus 232 equals 0 rightwards double arrow 3 n open parentheses n minus 8 close parentheses minus 29 open parentheses n minus 8 close parentheses equals 0 rightwards double arrow open parentheses 3 n minus 29 close parentheses open parentheses n minus 8 close parentheses equals 0 rightwards double arrow open parentheses 3 n minus 29 close parentheses equals 0 space o r space open parentheses n minus 8 close parentheses equals 0 rightwards double arrow 3 n equals 29 space o r space n equals 8 rightwards double arrow n equals 29 over 8 space o r space n equals 8 A s space n space c a n n o t space b e space a space f r a c t i o n comma space w e space h a v e comma space n equals 8 W e space n e e d space t o space f i n d space t h e space l a s t space t e r m comma l W e space k n o w space t h a t space l equals a plus open parentheses n minus 1 close parentheses d rightwards double arrow l equals 25 plus open parentheses 8 minus 1 close parentheses open parentheses negative 3 close parentheses rightwards double arrow l equals 25 plus 7 open parentheses negative 3 close parentheses rightwards double arrow l equals 25 minus 21 rightwards double arrow l equals 4
Answered by Expert 3rd September 2015, 9:21 AM
Rate this answer
  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10

You have rated this answer /10

Report an issue
Previous Question
Next Question
Your answer has been posted successfully!

Free related questions

RELATED STUDY RESOURCES :
KERALA Class-11-science QUESTION ANSWERS

Chat with us on WhatsApp