Given two lines, prove that if the slopes are the same and the y-intercepts are the same, then the lines coincide. assume two lines do not coincide (~q). then, either their slopes are different or their y-intercepts are different (~p). since ~q → ~p is true, p → q must be true. therefore, if the slopes and y-intercepts are the same, then two lines coincide. what type of proof is illustrated above? a. proof by contradiction b. proof by contraposition c. proof by direct method d. proof by law of detachment