Use a scalar projection to show that the distance from a point P1(x1, y1)

Use a scalar projection to show that the distance from a point P1(x1, y1) to the line ax+by+c=0 is |ax1+by1+c|/(a^2+b^2)^1/2

Use this formula to find the distance from the point to (-2, 3) the line 3x-4y+5=0