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    "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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    (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...


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    does it say that there is a right angle somewhere?
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    (Original post by TeeEm)
    does it say that there is a right angle somewhere?
    Yes


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    (Original post by jessyjellytot14)
    Yes


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    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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