LukasMcNeal Posted January 24, 2013 Report Share Posted January 24, 2013 Stuck on a question because I think my answer is bullshit! Its a geometric sequence 1st term = 2 Common ratio = 0.2 Worked out the 3rd term (was a question) = 0.016 Sum of the first 4 terms (was also a question) = 2.496 The bit I dont get is the sum to infinity... see picture. I got 2.5 but is that right? Quote Link to comment Share on other sites More sharing options...
TrialsIsHard Posted January 24, 2013 Report Share Posted January 24, 2013 (edited) Surely the sum to infinity is another way of saying the Nth term? Can't you use, n/2[2a+(n-1)d] ? Where n is infinity, a is the first term, and d is the common difference/ratio? Edit: I missed the point I think, common ratio is not common difference.. Edited January 24, 2013 by TrialsIsHard Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted January 24, 2013 Author Report Share Posted January 24, 2013 Nope thats for arithmetic sequences ans also not to infinty, n has to be a value, infinity cant be given as a number. The formula I used is right im just unsure of the answer! Quote Link to comment Share on other sites More sharing options...
Jake. Posted January 24, 2013 Report Share Posted January 24, 2013 I feel dumb now... 1 Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted January 24, 2013 Report Share Posted January 24, 2013 Can you not model it quickly in excel or something and see what the sum of the first 15, 30, 50 or whatever terms tends towards? Quote Link to comment Share on other sites More sharing options...
PaRtZ Posted January 24, 2013 Report Share Posted January 24, 2013 If i remember it right, theres an equation for it a(1 - rn ) 1 – r Should do it Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted January 24, 2013 Author Report Share Posted January 24, 2013 Thats for something else I cant think what though! I've used the correct equation just the answer looks too small! Quote Link to comment Share on other sites More sharing options...
casualjoe Posted January 24, 2013 Report Share Posted January 24, 2013 Multiply your 1st term by r squared, now try r cubed, now r^4, it should be the same as each term in your sequence. Quote Link to comment Share on other sites More sharing options...
Mule Posted January 24, 2013 Report Share Posted January 24, 2013 If your ever looking for Math help (quick answer check I use http://www.wolframalpha.com/ its a computational engine so it can process quite vague queries Quote Link to comment Share on other sites More sharing options...
dezmtber Posted January 25, 2013 Report Share Posted January 25, 2013 Where in the real world use would this type of maths be used. Since leaving school I have only ever used the times tables, area, and removing percentages. So what I wanna know other than being z maths teacher what jobs do you go for if your good at the math Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted January 25, 2013 Report Share Posted January 25, 2013 You're kidding, right? I'm struggling to think of much in the real world that doesn't use maths. You can't be serious... Quote Link to comment Share on other sites More sharing options...
PaRtZ Posted January 25, 2013 Report Share Posted January 25, 2013 Where in the real world use would this type of maths be used. Since leaving school I have only ever used the times tables, area, and removing percentages. So what I wanna know other than being z maths teacher what jobs do you go for if your good at the math bacteria growth? nuclear cell deteroriation? compound interest?... Quote Link to comment Share on other sites More sharing options...
J.KYDD Posted January 25, 2013 Report Share Posted January 25, 2013 Where in the real world use would this type of maths be used. Since leaving school I have only ever used the times tables, area, and removing percentages. So what I wanna know other than being z maths teacher what jobs do you go for if your good at the math Engineering and construction are the first two major industries which spring to mind Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted January 25, 2013 Report Share Posted January 25, 2013 I would also hazard a guess that the software in anything from a mobile phone to a set top box and maybe even a microwave involves maths and series' of some kind. As for using maths in jobs the list is pretty much endless. Any kind of engineering from Civil to F1, manufacturing, software development, computer science, electronics, accountancy (!)... surely even being a bike mechanic involves some maths in the form of geometry etc. Quote Link to comment Share on other sites More sharing options...
Mule Posted January 25, 2013 Report Share Posted January 25, 2013 Where in the real world use would this type of maths be used. Since leaving school I have only ever used the times tables, area, and removing percentages. So what I wanna know other than being z maths teacher what jobs do you go for if your good at the math Pretty sure you must use ratios from time to time. And your post must be a troll Also wether perdiction, robotics, being a pilot +all of the above aand im sure there are more Quote Link to comment Share on other sites More sharing options...
dezmtber Posted January 25, 2013 Report Share Posted January 25, 2013 (edited) addind subtracting and percentages yes, but not the fancy stuff i am on about. other than that there are calculators online for that Edited January 25, 2013 by dezmtber Quote Link to comment Share on other sites More sharing options...
LukasMcNeal Posted January 25, 2013 Author Report Share Posted January 25, 2013 That's like saying there's a calculator for just adding and subtracting. Before there was calculators you'd have to work it out, the same as anything else. You personally may never need to use something like this, it's not as complex as you think though this is only AS level maths. Quote Link to comment Share on other sites More sharing options...
casualjoe Posted January 25, 2013 Report Share Posted January 25, 2013 other than that there are calculators online for that You're right, calculators nowadays are amazing.. Quote Link to comment Share on other sites More sharing options...
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