y= 2x+4
Slope-intercept form
y=mx+b
Where:
m= slope
b= y-intercept
y=2x+4
Slope = m= 2
Perpendicular lines have negative reciprocal slopes.
So, the slope of the new line = -1/2
New equation:
y= -1/2x+b
Replace x,y by the point (4,2) and solve for b:
2 = -1/2(4)+b
2= -2 + b
2+2 = b
4 = b
New line equation:
y= -1/2x+4