Sum Series question

Q14 A) DONE!
B) NEED HELP

Doing some revision and question 14b.... how the hell did they get 210 as the answer...

(edited 4 years ago)

Question attached

Did you get 4r-1 as f(r)?

Original post by Yr_11_MATHS

Question attached

The series give:

10a+4b=36
21a+6b=78
So solve as simultaneous equations.

Did you get 4r-1 as f(r)?

The series give:

10a+4b=36
21a+6b=78
So solve as simultaneous equations.

Yes 4B is the one I'm having problems with

Did you get 4r-1 as f(r)?

The series give:

10a+4b=36
21a+6b=78
So solve as simultaneous equations.

4A i got 4r-1 but I don't know how to do 4B

Use the sum formula n(n+1) * 1/2 with n=10 and then subtract 10 for the 1 to 10 of -1

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