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# Coordinate geometry question watch

1. "The vertices of a triangle are the points P(3,C) , Q(9,2) and R(3C, 11). Find the value of C."

I have worked out the gradients of PQ and QR which are 2 - C divided by 6 and then 3 divided by C - 3 respectively. I am having difficulties working out C though. According to the mark scheme, C=4 but nothing ive done has got that answer. Ive tried putting the two gradients equal to eachother and rearranging but that hasnt worked...

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2. (Original post by jessyjellytot14)
"The vertices of a triangle are the points P(3,C) , Q(9,2) and R(3C, 11). Find the value of C."

I have worked out the gradients of PQ and QR which are 2 - C divided by 6 and then 3 divided by C - 3 respectively. I am having difficulties working out C though. According to the mark scheme, C=4 but nothing ive done has got that answer. Ive tried putting the two gradients equal to eachother and rearranging but that hasnt worked...

Posted from TSR Mobile
does it say that there is a right angle somewhere?
3. (Original post by TeeEm)
does it say that there is a right angle somewhere?
Yes

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4. (Original post by jessyjellytot14)
Yes

Posted from TSR Mobile
then you work out the 2 gradients in terms of the constant where appropriate.

if there is a right angle the gradients must multiply to -1 (that is the same as saying the gradients are negative reciprocals of each other.

(careful which gradients you work out)

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Updated: October 27, 2015
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