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sequences and series

the general term of a sequence is given by ur= (-1)r x5
1a) find out the first 6 terms of the sequence and describe it
For that i did 5,-5,5,-5,5,-5, but i can't describe it
1b) find the sum of of the series nΣr=1 ur
1bi) if n is even 2(5+-5) /2 =0(which is the answer
1bii) somehoe if n is odd the answer is -5 but i don't know how
1biii) also i'm confused how you can find an algebraic expression for the sum to n terms
Original post by realed
the general term of a sequence is given by ur= (-1)r x5
1a) find out the first 6 terms of the sequence and describe it
For that i did 5,-5,5,-5,5,-5, but i can't describe it
1b) find the sum of of the series nΣr=1 ur
1bi) if n is even 2(5+-5) /2 =0(which is the answer
1bii) somehoe if n is odd the answer is -5 but i don't know how
1biii) also i'm confused how you can find an algebraic expression for the sum to n terms

It would really help to upload an image of the question.
1a) if you plotted the terms, how would you describe it? Something about being 5 with alternating signs?
bii) use bi) and add the next odd term.
biii) Can you modify the original sequence/expression to give you corresponding sum values. Just write the sum to n below the nth term and think what is the transformation.

Note this is a geometric sequence.
(edited 1 year ago)
Reply 2
Original post by mqb2766
It would really help to upload an image of the question.
1a) if you plotted the terms, how would you describe it? Something about being 5 with alternating signs?
bii) use bi) and add the next odd term.
biii) Can you modify the original sequence/expression to give you corresponding sum values. Just write the sum to n below the nth term and think what is the transformation.

Note this is a geometric sequence.

okay something i realised is that the sequence should be -5,5,-5,5,-5,5
seconfly to make it work you have to use (-1)n so i did -5/2+5/2(-1)n
Original post by realed
okay something i realised is that the sequence should be -5,5,-5,5,-5,5
seconfly to make it work you have to use (-1)n so i did -5/2+5/2(-1)n


Im not sure what you mean by to make it (what?) work? But you can do it in an adhoc fashion as mentioned above or use the geometric formula, so if you're having problems doing either can you post an image of the original question and your working?
(edited 1 year ago)
Reply 4
Original post by mqb2766
It would really help to upload an image of the question.
1a) if you plotted the terms, how would you describe it? Something about being 5 with alternating signs?
bii) use bi) and add the next odd term.
biii) Can you modify the original sequence/expression to give you corresponding sum values. Just write the sum to n below the nth term and think what is the transformation.

Note this is a geometric sequence.

okay something i realised is that the sequence should be -5,5,-5,5,-5,5
seconfly to make it work you have to use (-1)n so i did -5/2+5/2(-1)n
Original post by realed
okay something i realised is that the sequence should be -5,5,-5,5,-5,5
seconfly to make it work you have to use (-1)n so i did -5/2+5/2(-1)n


Thats the same as the previous post so Im guessing thats your series? Personally, Id do it both adhoc as the question seems to be leading you down, but also using the series formula. Good practice both ways. But again, can you upload a pic of the question, in the OP preferably.
Reply 6
how

Original post by mqb2766
Thats the same as the previous post so Im guessing thats your series? Personally, Id do it both adhoc as the question seems to be leading you down, but also using the series formula. Good practice both ways. But again, can you upload a pic of the question, in the OP preferably.
Original post by realed
how

How what?
Reply 8
can you out the photo on here
Original post by realed
can you out the photo on here


When you reply, the camera icon on the toolbar at the top is "upload image".

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