Find coordinates of the point, which when joined with (c1,c2) forms a line that is parallel to the line joining (a1,a2) and (b1,b2)?

1 Answer
Sep 26, 2016

Any point lying on (b2b1)(xc1)(yc2)(a2a1)=0 when joined with (c1,c2) would form a line parallel to the line joining (a1,a2) and (b1,b2).

Explanation:

The slope of a line passing through (a1,a2) and (b1,b2) is b2b1a2a1

The equation of a line with a slope m and passing through (x1,y1) is yy1=m(xx1)

As the slope of the line parallel to above too would be b2b1a2a1 and as it passes through (c1,c2), its equation would be

yc2=b2b1a2a1(xc1) or

(b2b1)(xc1)(yc2)(a2a1)=0

Hence any point lying on (b2b1)(xc1)(yc2)(a2a1)=0 will satisfy the given condition, i.e. when joined with (c1,c2) would form a line parallel to the line joining (a1,a2) and (b1,b2).