# A level Maths help

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An engineer is making a circular disc.

A model of the disc is drawn as a circle on a set of axes such that it passes

through coordinate points P (–1, –1), Q (5, k) and R(7, 3)

Given that angle PRQ is 90°, find the value of k and the area of the disc

I can’t figure out how to do this I drew a diagram and I don’t see a right angle could someone please show me how to do it

A model of the disc is drawn as a circle on a set of axes such that it passes

through coordinate points P (–1, –1), Q (5, k) and R(7, 3)

Given that angle PRQ is 90°, find the value of k and the area of the disc

I can’t figure out how to do this I drew a diagram and I don’t see a right angle could someone please show me how to do it

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#3

(Original post by

An engineer is making a circular disc.

A model of the disc is drawn as a circle on a set of axes such that it passes

through coordinate points P (–1, –1), Q (5, k) and R(7, 3)

Given that angle PRQ is 90°, find the value of k and the area of the disc

I can’t figure out how to do this I drew a diagram and I don’t see a right angle could someone please show me how to do it

**Anonymous9795**)An engineer is making a circular disc.

A model of the disc is drawn as a circle on a set of axes such that it passes

through coordinate points P (–1, –1), Q (5, k) and R(7, 3)

Given that angle PRQ is 90°, find the value of k and the area of the disc

I can’t figure out how to do this I drew a diagram and I don’t see a right angle could someone please show me how to do it

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#4

**Anonymous9795**)

An engineer is making a circular disc.

A model of the disc is drawn as a circle on a set of axes such that it passes

through coordinate points P (–1, –1), Q (5, k) and R(7, 3)

Given that angle PRQ is 90°, find the value of k and the area of the disc

I can’t figure out how to do this I drew a diagram and I don’t see a right angle could someone please show me how to do it

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(Original post by

Anything about semicircles and right angles ring any bells?

**DFranklin**)Anything about semicircles and right angles ring any bells?

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(Original post by

are you sure it is PRQ that is a right angle??

**df1**)are you sure it is PRQ that is a right angle??

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#7

(Original post by

Nope I’m a first year so haven’t done anything in a while the only thing I managed to come up with is (5,7) but that’s where I get confused about where the circle is on the graph I assumed that r was the midpoint and p was on the circumference but that would mean that (5,7) would just be along the diameter.

**Anonymous9795**)Nope I’m a first year so haven’t done anything in a while the only thing I managed to come up with is (5,7) but that’s where I get confused about where the circle is on the graph I assumed that r was the midpoint and p was on the circumference but that would mean that (5,7) would just be along the diameter.

Since PRQ is a right angle, it follows that PQ is a diameter. Hence work out radius and area.

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#8

**Anonymous9795**)

An engineer is making a circular disc.

A model of the disc is drawn as a circle on a set of axes such that it passes

through coordinate points P (–1, –1), Q (5, k) and R(7, 3)

Given that angle PRQ is 90°, find the value of k and the area of the disc

I can’t figure out how to do this I drew a diagram and I don’t see a right angle could someone please show me how to do it

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(Original post by

Agree with (5,7) as the position of Q. All of P,Q,R are on the circumference.

Since PRQ is a right angle, it follows that PQ is a diameter. Hence work out radius and area.

**ghostwalker**)Agree with (5,7) as the position of Q. All of P,Q,R are on the circumference.

Since PRQ is a right angle, it follows that PQ is a diameter. Hence work out radius and area.

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#10

(Original post by

Thanks for your help I got confused with where the circle was but now l understand

**Anonymous9795**)Thanks for your help I got confused with where the circle was but now l understand

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Thanks but I don’t think that q can be (5,10.75) because it wouldn’t be on the line perpendicular (y=-2x+17) to PR (y=0.5x+0.5) thus making PRQ not 90°

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#12

(Original post by

Thanks but I don’t think that q can be (5,10.75) because it wouldn’t be on the line perpendicular (y=-2x+17) to PR (y=0.5x+0.5) thus making PRQ not 90°

**Anonymous9795**)Thanks but I don’t think that q can be (5,10.75) because it wouldn’t be on the line perpendicular (y=-2x+17) to PR (y=0.5x+0.5) thus making PRQ not 90°

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#13

(Original post by

yeah i guess that would make my answer wrong then, I can't think of another way to do it but I might have made a numerical or simplifying error somewhere so you could always retry it and be more careful than me and see if it gets an answer that works lol

**df1**)yeah i guess that would make my answer wrong then, I can't think of another way to do it but I might have made a numerical or simplifying error somewhere so you could always retry it and be more careful than me and see if it gets an answer that works lol

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#14

**Anonymous9795**)

Thanks but I don’t think that q can be (5,10.75) because it wouldn’t be on the line perpendicular (y=-2x+17) to PR (y=0.5x+0.5) thus making PRQ not 90°

So now you know the coordinates of all the points you can work out the diameter, and hence the radius, and hence the area as suggested earlier

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(Original post by

actually you could try a method of simultaneous equations of the lines PR and QR to solve for K

**df1**)actually you could try a method of simultaneous equations of the lines PR and QR to solve for K

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