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Coordinate geometry question help! (: watch

1. The vertices of a triangle are the points P(3,c), Q(9,2) and R(3c,11) where c is a constant.
Given that angle PQR = 90

a) Find the value of c.

Thank you
2. (Original post by Dinaa)
The vertices of a triangle are the points P(3,c), Q(9,2) and R(3c,11) where c is a constant.
Given that angle PQR = 90

a) Find the value of c.

Thank you
PQR = 90, so PQ is perpendicular to QR.

What's the gradient of PQ, as a function of c?
Similarly QR.
What do you know about a relationship between the gradients of perpendicular lines?
3. One moment, I think this is right but my co-ordinate geometry is a bit rusty.
4. (Original post by Dinaa)
The vertices of a triangle are the points P(3,c), Q(9,2) and R(3c,11) where c is a constant.
Given that angle PQR = 90

a) Find the value of c.

Thank you

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