1.

Equation of a line passing through point A(x1, y1) and having slope m (see Fig.)  is y - y1 =  m(x - x1)

Answer»

Suppose P(x, y) is any point on the given line.   Then, the slope of the line is  y - y1/x - x1 = m

Therefore,

y - y1 =  m(x - x1

Conversely, let Q(x', y') be a point such that

y' - y1 =  m(x - x1)

 y' - y1/x - x1 = m (slope of the line) 

This implies that the line (bar)AQ coincides with the given line which, in turn, implies that Q lies on the given line. Therefore, equation of the line is y - y1 =  m(x - x1). 



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