GMATPREP: Co-Ordinate
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to know if the two lines are perpendicular, we need to know if the two slopes are the negative reciprocal of the other. So we need to know both slopes to come up with an answer.
I) We know that like k intersects line m at (1,-1) which lies on line m. So we know have two points for line k and can determine K's slope. But we don't know anything about M's slope. so INSUFF.
II) We now learn another point on like k... so we can determine its slope (and will see that they intersect at (1,-1). But we don't know anything about M's slope.. so INSUFF.
Together?
Both I and II tell us k's slope, but neither tell us anything about M's slope... So together they are INSUFF.
Choose E.
I) We know that like k intersects line m at (1,-1) which lies on line m. So we know have two points for line k and can determine K's slope. But we don't know anything about M's slope. so INSUFF.
II) We now learn another point on like k... so we can determine its slope (and will see that they intersect at (1,-1). But we don't know anything about M's slope.. so INSUFF.
Together?
Both I and II tell us k's slope, but neither tell us anything about M's slope... So together they are INSUFF.
Choose E.