find the equation of the line though C(5, 8) perpendicular to AB. AB is 8x+5y-1=0
8x+5y-1=0
5y=-8x+1
y=(-8x+1)/5
gradient = -8/5
gradient of perpendicular is 5/8 also through (5,8)
y-8=(5/8)(x-5)
8y-64=5x-25
5x-8y-25+64=0
5x-8y+39=0
you need to check it :)
