It is also possible to add the terms form (a+4d) to (a+7d) together and equalizing them to 114.The same method applies for the second series. Add from the term (a+11d) to (a+14d) and equalize to 198. The key idea behind this is that the sum of that particular term is always one less in the series. For example:- S5 will be equal to a to (a+4d)Th term and not a to (a+5d)Th term
You don't have to use the formula for this particular question , right? Because I used the nth term so : (a+4d)+(a+5d)+(a+6d)+(a+7d)=4a + 22d=114 and the same for the other part. Also you only said "inclusive" for the first part of the question, so if this happens in the real thing should we assume it for the next part?
Yup I did it this method as well. But it doesn't matter, either method is correct. Having alternative ways to solve a problem is always good. Regarding your question about the "inclusive" part, yup it goes for both parts. I assumed so anyway lol
Which one requires more thought, solving this problem using the arithmetic sequence formula or the arithmetic sum formula? In my opinion I think the sequence formula is much simpler to use.
I think you've got the simultaneous equations wrong, the n over two you have used for the 12th term you've written as eleven and so has made the whole answer wrong, the final value for d is 3, a is 27 and 21st term = 87
It is also possible to add the terms form (a+4d) to (a+7d) together and equalizing them to 114.The same method applies for the second series. Add from the term (a+11d) to (a+14d) and equalize to 198. The key idea behind this is that the sum of that particular term is always one less in the series. For example:- S5 will be equal to a to (a+4d)Th term and not a to (a+5d)Th term
You never cease to make me understand. Thank you man 🙏
It's great to have your support. Thank you.
Can confirm, is advocating genocide - 0:31
You don't have to use the formula for this particular question , right? Because I used the nth term so : (a+4d)+(a+5d)+(a+6d)+(a+7d)=4a + 22d=114 and the same for the other part. Also you only said "inclusive" for the first part of the question, so if this happens in the real thing should we assume it for the next part?
Yup I did it this method as well. But it doesn't matter, either method is correct. Having alternative ways to solve a problem is always good. Regarding your question about the "inclusive" part, yup it goes for both parts. I assumed so anyway lol
Which one requires more thought, solving this problem using the arithmetic sequence formula or the arithmetic sum formula? In my opinion I think the sequence formula is much simpler to use.
Itms the sum of 12th term not 11 so is this whole thing wrong ?
FIRST! And great video thanks!
cheers
How many marks was this worth?
I think 5 marks
Once you've done the Binomial CD stuff of the A level course, this becomes fairly obvious imo.
I think you've got the simultaneous equations wrong, the n over two you have used for the 12th term you've written as eleven and so has made the whole answer wrong, the final value for d is 3, a is 27 and 21st term = 87
South North No I haven't made a mistake. It should be the S11th sum. S15 - S12 gives the sum of the 12,13, 14 and 15th terms.
Also to be honest I thought the "Beastie" problem would've been much complex and fun, but was unfortunately left disappointed😞