Philip P. answered 04/16/16
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Effective and Patient Math Tutor
A = (xA,yA) = (-2,1)
B = (xB,yB) = (2,-3)
Let point P represent the point on AB such that AP:PB = 3:4. In a ratio of 3:4, you are dividing the line into 3+4 = 7 parts. Line AP is 3/7 of AB, line PB is 4/7 of AB. Since we want AP = 3/7 of AB, we use the ratio r = 3/7. The formula for point P is:
P = (xP,yP) = ( xA+r(xB-xA), yA+r(yB-yA) )
P = (-2+(3/7)(2 - -2), 1+(3/7)(-3 - 1))
p = (-2+12/7, 1-12/7)
p = (-2/7, -5/7)