Let the coordinates of foot of perpendicular be A(α,β) from the point P(2,3) (say) on line y=3x+4
Slope of AP, m1=α−2β−3
Slope of given line, m2=3
Since, both are perpendicular. ∴m1×m2=−1 ⇒α−2β−3×3=−1 ⇒3β=−α+11…(i)
Also, the point A(α,β) is on the given line.
So, A(α,β) satisfy the equation of the line. ∴β=3α+4…(ii)
On solving (i) and (ii), we get α=−101, β=1037
So, coordinates of foot of perpendicular is (10−1,1037).