For perpendicular lines, m1m2 = -1 or m2 = -1/m1; where m1 and m2 are the slopes of the lines.
Here line 1 is 2x - y - 7 = 0
y = 2x - 7; Hence m1 = 2
m2 = -1/2
Required equation y - y1 = m2(x - x1)
y - (-1) = -1/2(x - 4)
y + 1 = -1/2x + 2
y = -1/2x + 2 - 1
y = -1/2x + 1