Naiya Posted May 6, 2011 Report Share Posted May 6, 2011 Oh my god. I answered A = 50, B = pi/10 and C = 50. Nooooo. My full marks is gone now!okkie..... i am not sure whether i did A=(-50)..... i did A=50 i guess.... but why will there be a minus sign??? Reply Link to post Share on other sites More sharing options...
lighthuntz0r Posted May 6, 2011 Report Share Posted May 6, 2011 minus because the function is sort of reflected around x axis (starts at low and goes to high, opposite of normal cosine function which starts at high) Reply Link to post Share on other sites More sharing options...
Naiya Posted May 6, 2011 Report Share Posted May 6, 2011 minus because the function is sort of reflected around x axis (starts at low and goes to high, opposite of normal cosine function which starts at high)hmmm..... right!! but then the there should also exist the horizontal translation in the equation, shouldn't it?? because even if you reflect it then too the does not exactly start from the origin like sin.... Reply Link to post Share on other sites More sharing options...
lighthuntz0r Posted May 6, 2011 Report Share Posted May 6, 2011 It does once you add a +50 vertical translation. Reply Link to post Share on other sites More sharing options...
I`m Potato Posted May 6, 2011 Report Share Posted May 6, 2011 What's the formula to obtain the value of A? I just guessed haha. Reply Link to post Share on other sites More sharing options...
Cynthia Posted May 6, 2011 Report Share Posted May 6, 2011 What's the formula to obtain the value of A? I just guessed haha.It's (y-coordinate of min point + y-coordinate of max point) / 2, then you need to add a minus if there's a reflection. Reply Link to post Share on other sites More sharing options...
lexie Posted May 6, 2011 Report Share Posted May 6, 2011 I think it probably depends more on grade boundaries than the grader. keep in mind you should get follow through points if you did a problem right using a wrong value at the beginning, and that you do get points for a correct method even if you didn't quite get to the end of questions. Especially for a question where you just made a sign error, you should get points if you did everything else right. It's easier said than done but try not to worry, instead focus on studying for your other exams so that even if you maths score isn't a 5, you can pull your score up in other subjects 2 Reply Link to post Share on other sites More sharing options...
Ika Lob Posted May 6, 2011 Report Share Posted May 6, 2011 I am almost sure that the value of A can equal 50 OR -50. That's because the cosine function does not "start" at a specific point (t=0). It's continuous, having multiple revolutions. Therefore, although after t=0, the curve was going upwards (and since it is a cosine function, you would consider this to be negative, since cos goes upwards), after t=2, the curve starts going down, therefore you can also say that A= 50. The only variable being affected by a cosine is the horizontal shift. Otherwise, the amptitude, period and vertical shift are always the same for both cosine and sine functions.By the way, does anyone remember what question 9 was about? Number 8 was on transforming functions and finding derivatives and question 10 was the ferris wheel. Reply Link to post Share on other sites More sharing options...
Cynthia Posted May 6, 2011 Report Share Posted May 6, 2011 @Ika Lob: no, you're actually not right in that, as there was no horizontal shift of the graph (if there had been, it would've been possible); in this case, however, x=0 is always the max point unless it's been reflected. Reply Link to post Share on other sites More sharing options...
000 Posted May 6, 2011 Report Share Posted May 6, 2011 By the way, does anyone remember what question 9 was about? Number 8 was on transforming functions and finding derivatives and question 10 was the ferris wheel.wasn't question 9 the probability dice one? Reply Link to post Share on other sites More sharing options...
iber2011 Posted May 6, 2011 Report Share Posted May 6, 2011 What's the formula to obtain the value of A? I just guessed haha.It's (y-coordinate of min point + y-coordinate of max point) / 2, then you need to add a minus if there's a reflection.I can't seem to remember that question! Can you please remind me? Reply Link to post Share on other sites More sharing options...
Cynthia Posted May 6, 2011 Report Share Posted May 6, 2011 @iber 2011; It's the Ferris Wheel question, finding A, B and C values for A cos (B*t) + C Reply Link to post Share on other sites More sharing options...
Ika Lob Posted May 6, 2011 Report Share Posted May 6, 2011 @Ika Lob: no, you're actually not right in that, as there was no horizontal shift of the graph (if there had been, it would've been possible); in this case, however, x=0 is always the max point unless it's been reflected.I think you're right. Are you saying that since they did not give even a variable for the horizontal shift, it is assumed to be zero?It was A cosBx + C. So if it had been A cosB(x-D) + C and they asked us to find A, B and C, then it could have been A= 50 or -50 (given that we could alter the horizontal shift). Reply Link to post Share on other sites More sharing options...
shreyaa Posted May 6, 2011 Report Share Posted May 6, 2011 Our maths teacher had told us the value of amplitude of sin or cos cannot be negative.. So i got the value of A= 50 and the value of c= -50 Reply Link to post Share on other sites More sharing options...
Ika Lob Posted May 6, 2011 Report Share Posted May 6, 2011 Our maths teacher had told us the value of amplitude of sin or cos cannot be negative.. So i got the value of A= 50 and the value of c= -50Yes but A does not = amplitude. Just like B does not equal the period. 2pie/B equals the period and the absolute value of A is the amplitude. Reply Link to post Share on other sites More sharing options...
shreyaa Posted May 6, 2011 Report Share Posted May 6, 2011 the 1st question in section-B related to calculus.. i got the area as 1/6did anybody else get the same answer? Reply Link to post Share on other sites More sharing options...
Cynthia Posted May 6, 2011 Report Share Posted May 6, 2011 the 1st question in section-B related to calculus.. i got the area as 1/6did anybody else get the same answer? Got the same one I think. It seemed suspiciously small but then again the limit was very small as well and I couldn't find a mistake in my calculations... Reply Link to post Share on other sites More sharing options...
IBMay2011 Posted May 6, 2011 Report Share Posted May 6, 2011 the 1st question in section-B related to calculus.. i got the area as 1/6did anybody else get the same answer? I also got 1/6. How did you do it? I did area of graph - area of triangle. Reply Link to post Share on other sites More sharing options...
Cynthia Posted May 6, 2011 Report Share Posted May 6, 2011 @IBMay2011 I did the same thing. Reply Link to post Share on other sites More sharing options...
butters Posted May 6, 2011 Report Share Posted May 6, 2011 1/6 is right. im sure about that Reply Link to post Share on other sites More sharing options...
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