# Maths

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Thread starter 4 months ago
#1
Please can u help me with this question
22) C is a circle with centre the origin.
A tangent to C passes through the points (–20, 0) and (0, 10)
Work out an equation of C.
You must show all your working.
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4 months ago
#2
(Original post by raidas0001)
Please can u help me with this question
22) C is a circle with centre the origin.
A tangent to C passes through the points (–20, 0) and (0, 10)
Work out an equation of C.
You must show all your working.
What have you done so far, and where are you stuck?
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Thread starter 4 months ago
#3
(Original post by ghostwalker)
What have you done so far, and where are you stuck?
x^2+y^2=r^2
gradint=(10-0)/(0--20)=0.5
y=mx+c
y=0.5x+c
0=0.5(-20)+c
0=-10+c
c=10
y=0.5x+10
1/2 x -2 =-1
y=2x+c
10=2(0)+c
c=10
r=2x+10
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4 months ago
#4
(Original post by raidas0001)
x^2+y^2=r^2
gradint=(10-0)/(0--20)=0.5
y=mx+c
y=0.5x+c
0=0.5(-20)+c
0=-10+c
c=10
y=0.5x+10
I can see here that you're worked out the equation of the tangent.

1/2 x -2 =-1
Looks is if you're finding the gradient of a perpendicular line

y=2x+c
10=2(0)+c
c=10
r=2x+10
Your gradient seems to have changed from -2 to 2.

And you're finding a perpendicular line going through (0,10). Don't think that's going to be very useful.

If you want the perpendicular to be a radius, then it needs to go through the centre of the circle - viz. the origin.

You might find a diagram helpful, if you haven't already drawn one.

I presume you're then finding the intersection of the two lines, and hence the radius?
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1 month ago
#5
Where did you get this question from?Was it from GCSE past paper....thank you.
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