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OCR (not MEI) C2 - Wednesday 20th May 2015 watch

1. y^2= 27
log3(y^2)= log3(27)
2log3(y) = log3(3) + log3(3) + log3(3) *move power of y in front of log
* 27= 3x3x3 so break apart using log rules
2log3(y) = 3 *loga(a) =1
log3(y)= 3/2
2. What happens when you are doing trigonometry and you get a negative angle ?
What happens when you are doing trigonometry and you get a negative angle ?
Do you have a question as an example?
Where did you get the 272 or the log after it ?
Sorry I forgot to press enter :P,
y²=27
log3y² = log327
2log3y = 3
log3y = 1.5
5. https://68baf9f6baae001b7abe18b6e880...20C2%20OCR.pdf
Question 5(ii) When I got my sin angles ,I got sin^-1(-2/5) which got me a negative angle.
https://68baf9f6baae001b7abe18b6e880...20C2%20OCR.pdf
Question 5(ii) When I got my sin angles ,I got sin^-1(-2/5) which got me a negative angle.
use cast diagram to find the positive angle then keep going like a normal question like this
7. Quick question ?Do we have to show the CAST diagram ?Can we draw two ,one for each angle Im finding ?
https://68baf9f6baae001b7abe18b6e880...20C2%20OCR.pdf
Question 5(ii) When I got my sin angles ,I got sin^-1(-2/5) which got me a negative angle.
That is no problem. Can you please give me a min to write it up
9. Can anyone help me with this log question please?

Find the roots of the equation 2log(base4)x - log(base4)(-7x+3)=-1/2?

I have got to 2x^2 + 7x - 3 = 0 but you have to use the quadratic formula to factorise this and I do not get the correct answer...have I made a mistake?

Thanks!
https://68baf9f6baae001b7abe18b6e880...20C2%20OCR.pdf
Question 5(ii) When I got my sin angles ,I got sin^-1(-2/5) which got me a negative angle.
11. (Original post by Issy :))
I use the CAST method . Im confused ,I thought we woud add 180 to 19.5.For the engative angle,did you substract from 180 ?
I use the CAST method . Im confused ,I thought we woud add 180 to 19.5.For the engative angle,did you substract from 180 ?
Do you have the answers? I have been doing maths all day so might have messed it up. My brain is literally fried.
13. (Original post by giantbecky)
Can anyone help me with this log question please?

Find the roots of the equation 2log(base4)x - log(base4)(-7x+3)=-1/2?

I have got to 2x^2 + 7x - 3 = 0 but you have to use the quadratic formula to factorise this and I do not get the correct answer...have I made a mistake?

Thanks!
I got that equation as well, can you tell what paper this question is from.
14. (Original post by Sahil_)
I got that equation as well, can you tell what paper this question is from.
It's not from a paper, it's from this revision guide/textbook...I can tell you the answers if you want?
I thought maybe the answers were wrong but when I put them back into the original log equation they give -1/2
15. No, I was right, I just got fed up writing out all the answers halfway through. I really can't explain the cast method as I have always been taught the graph way. Let me think a mo and see if I can explain it
16. (Original post by giantbecky)
It's not from a paper, it's from this revision guide/textbook...I can tell you the answers if you want?
I thought maybe the answers were wrong but when I put them back into the original log equation they give -1/2
If you put the answers from the textbook into the equation does is also give -1/2?
17. Ok, so the 19.5 value is positive so can only be in the first and second quadrant yes (CAST so only A and S) therefore is 180-19.5.
The negative value, for sin to be negative it must be in the 3rd or 4th quadrant. Therefore, ignore the negative when typing into the calc then do 360-23.6 and 180+23.6
That is using the cast diagram (needed a min to jog my memory of the method)

I use the CAST method . Im confused ,I thought we woud add 180 to 19.5.For the engative angle,did you substract from 180 ?
18. (Original post by Sahil_)
If you put the answers from the textbook into the equation does is also give -1/2?
the answers are 3 and 1/2 and actually I just tried 1/2 and I don't think that works as -7x1/2 +3 = -1/2 and you can't take logs of negative numbers...

So maybe the textbook is wrong?
19. (Original post by Issy :))
Ok, so the 19.5 value is positive so can only be in the first and second quadrant yes (CAST so only A and S) therefore is 180-19.5.
The negative value, for sin to be negative it must be in the 3rd or 4th quadrant. Therefore, ignore the negative when typing into the calc then do 360-23.6 and 180+23.6
That is using the cast diagram (needed a min to jog my memory of the method)
Thank you so much !

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