two perpendicular lines have slopes that are negative reciprocals of each other, that is, if one slope is a/b, the other is -b/a
the first line 5x+2y=20, 2y=-5x +20, y=-5/2 x+10, the slope is -5/2, so the perpendicular line's slope is 2/5
the equation in point-slope form is (y-2)=(2/5)(x-5)
in slope-intercept form: y=(2/5)x
in standard form: 2x-5y=0
