Is ab perpendicular to cd? Explain. Yes, because the slope of ab is 5/3 and the slope of cd is -3/5. Yes, because the slope of ab is 4/3 and the slope of cd is -3/4. No, because the slope of ab is 5/3 and the slope of cd is -3/4. No, because the slope of ab is 4/3 and the slope of cd is -3/5.