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C1 maths, I'm having some problems with 11(iii). Any ideas?



Remember that ABCD is a rectangle. Therefore you should have right angle at each corner, and each pair of lines to make that right angle are perpendicular.
Because it's a rectangle, k (which is a y coordinate) will share it's value with at least one of the other points. Therefore it could be 4 or -3. Drawing it out really helps to show it's in line with the two coordinates.
Original post by The.One.And.Only
Because it's a rectangle, k (which is a y coordinate) will share it's value with at least one of the other points. Therefore it could be 4 or -3. Drawing it out really helps to show it's in line with the two coordinates.


Apologies The.One.And.Only, but I disagree. A rectangle could be formed with the coordinates ( 0 , 2 ), ( 3 , 1 ), ( 4.8 , 6.4 ), (1.8 , 7.4 ) and there are no values that are shared with any other points. Whilst you could be right if the rectangle is parallel to either axis, this one is not.

Bearing in mind that this is a 5 mark question, the only way to solve this is to form a quadratic. Once there, you get the solutions that k=3 or k=-2.
(edited 5 years ago)
Thanks guys for your fast feedback! Working on it again now.

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