2 x 1.5 is 3 - 1 is 2 that is right over there. so all of a sudden he was able to bridge this gap or this relationship between algebra and geometry. we can now visualize all of the x and y pairs that satisfy this equation right over here. and so he is responsible for making this bridge and that's why that co-ordinates that we use to specify these points are called 'cartesian coordinates' and as we'll see and first type of equations we will study our equations of this form over here and in a traditional algebra curriculum. they're called linear equations...