



 
Hi Alister, I can draw a diagram for you which hopefully will point you in the right direction. L_{1} and L_{2} are perpendicular and P is their point of intersection. R is a point on L_{1} different from P and Q is such that PQ is horizontal and QR is vertical. Extend QP to T so that TP = QR. The vertical line through T meets L_{2} at S. What is the slope of L_{1}? Penny  


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