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# C1 - Differentiation and circles watch

1. Question 8 ii)

I was just wondering why cant you put y = 3x + 4

in to the equation

( x + 3 ) ^2 + ( y- 2 ) ^2 = 17^2

I did this and got ( x + 3 )^2 + (3x + 2 )^2 = 17^2

took the sqrt of both sides and ended up with x = 3 which is wrong...

Also the 11iii)

The first part x = 5/2

the second part x lies between .... -11/3 x < 3

Final answer = 5/2 less than or equal to x < 3

I was just wondering the final answer does not give the complete range of x values as x can 1 or 2. Is this correct?
2. Would be nice if you could perhaps post the question?
3. (Original post by IShouldBeRevising_)
Question 8 ii)

I was just wondering why cant you put y = 3x + 4

in to the equation

( x + 3 ) ^2 + ( y- 2 ) ^2 = 17^2

I did this and got ( x + 3 )^2 + (3x + 2 )^2 = 17^2

took the sqrt of both sides and ended up with x = 3 which is wrong...
Square rooting both sides is horribly messy, far better to expand and solve the quadratic.
4. (Original post by IShouldBeRevising_)
Question 8 ii)

I was just wondering why cant you put y = 3x + 4

in to the equation

( x + 3 ) ^2 + ( y- 2 ) ^2 = 17^2

I did this and got ( x + 3 )^2 + (3x + 2 )^2 = 17^2

took the sqrt of both sides and ended up with x = 3 which is wrong...

Also the 11iii)

The first part x = 5/2

the second part x lies between .... -11/3 x < 3

Final answer = 5/2 less than or equal to x < 3

I was just wondering the final answer does not give the complete range of x values as x can 1 or 2. Is this correct?
One thing I did notice with your working even though I don't know the question is that you've made quite a misconception here.

You did which is incorrect

5. (Original post by justinawe)
One thing I did notice with your working even though I don't know the question is that you've made quite a misconception here.

You did which is incorrect

Yeah I thought they were equal

(Original post by joostan)
Square rooting both sides is horribly messy, far better to expand and solve the quadratic.

(Original post by justinawe)
Would be nice if you could perhaps post the question?
I always forget to add the question..
http://www.ocr.org.uk/Images/57769-q...hematics-1.pdf
6. (Original post by IShouldBeRevising_)
Yeah I thought they were equal

I always forget to add the question..
http://www.ocr.org.uk/Images/57769-q...hematics-1.pdf
This appears to be the wrong paper no q11 and q8 is different
7. (Original post by joostan)
This appears to be the wrong paper no q11 and q8 is different

http://www.ocr.org.uk/Images/59551-q...hematics-1.pdf
8. For q8 do as we suggested above.
As for q11 part i) is to find the perimeter in terms of x. You appear to have solved for x. . .
EDIT: I see what you mean now just a mo...
No x cannot equal 1 or 2
9. For 11iii) your answer is correct and gives the complete range of x values that satisfy the both inequalities. x cannot be 1 or 2 as the perimeter would not be at least 39 m if that were the case.
10. (Original post by justinawe)
For 11iii) your answer is correct and gives the complete range of x values that satisfy the both inequalities. x cannot be 1 or 2 as the perimeter would not be at least 39 m if that were the case.

(Original post by joostan)
For q8 do as we suggested above.
As for q11 part i) is to find the perimeter in terms of x. You appear to have solved for x. . .
EDIT: I see what you mean now just a mo...
No x cannot equal 1 or 2
Ok thank you guys I get it now
11. (Original post by IShouldBeRevising_)
Ok thank you guys I get it now
Good

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