Question marks are what i need filled in, will give brainliest. given: a b c d is a square. prove: the diagonals of a b c d are perpendicular. the coordinates of square abcd are a(0, 0) , b(a, 0) , , a), and d(0, the slope of ac¯¯¯¯¯ , when simplified, is equal to . the slope of bd¯¯¯¯¯, when simplified, is equal to −1 . the product of the slopes is equal to . therefore, ac¯¯¯¯¯ is perpendicular to bd¯¯¯¯¯.