Year 12s: what will be the first way you research your future options? >>

Year 12s: what will be the first way you research your future options? >>

Year 12s: what will be the first way you research your future options? >>

Tangent to a circle?

9ii) http://www.ocr.org.uk/download/pp_11_jan/ocr_61425_pp_11_jan_gce_472101.pdf

Basically i substitued y=k into the circle equation i got up to

x^2 -8x +k^2 -2k = 3

Firstly, that just looks wrong..

What do i actually do??

(edited 11 years ago)

Original post by Abed1993

9ii) http://www.ocr.org.uk/download/pp_11_jan/ocr_61425_pp_11_jan_gce_472101.pdf

Basically i substitued y=k into the circle equation i got up to

x^2 -8x +k^2 -2k = 38

Firstly, that just looks wrong..

What do i actually do??

x^2 -8x +k^2 -2k = 38 \implies x^2 - 8x + (k^2 -2k -38)=0

The above equation is a quadratic, solve it by using the discriminant.

Remember tangent intersects a circle at only one point, hence,

b^2 - 4ac=0

Draw a diagram, and consider what the line y= k, for any k looks like... e.g. y =3, y= -5.4, etc.

The answer should then become obvious.

Hint: You will need to use your answers to 9i) to answer this.

Edit: I suppose the discriminant method could also work.

(edited 11 years ago)

that is fine

tangent means the equation has how many solutions

OP

Original post by raheem94

x^2 -8x +k^2 -2k = 38 \implies x^2 - 8x + (k^2 -2k -38)=0

The above equation is a quadratic, solve it by using the discriminant.

Remember tangent intersects a circle at only one point, hence,

b^2 - 4ac=0

Oh i see! Tangent to a curve/circle will always have equal roots?

Original post by Abed1993

Oh i see! Tangent to a curve/circle will always have equal roots?

Tangent to a circle always has equal roots.

OP

Original post by raheem94

Tangent to a circle always has equal roots.

oh cool!

Do you know where i can get the jan 2012 ocr c1 paper??
been looking for it all over the internet! can't seem to find it :/

Original post by Abed1993

oh cool!

Do you know where i can get the jan 2012 ocr c1 paper??
been looking for it all over the internet! can't seem to find it :/

No idea!

Original post by Abed1993

oh cool!

Do you know where i can get the jan 2012 ocr c1 paper??
been looking for it all over the internet! can't seem to find it :/

Your school should have a copy or at least the means to get a copy of the paper.

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