One line passes through the points \blueD{(-3,-1)}(−3,−1)start color #11accd, left parenthesis, minus, 3, comma, minus, 1, right parenthesis, end color #11accd and \blueD{(1,-9)}(1,−9)start color #11accd, left parenthesis, 1, comma, minus, 9, right parenthesis, end color #11accd. Another line passes through points \greenD{(1,4)}(1,4)start color #1fab54, left parenthesis, 1, comma, 4, right parenthesis, end color #1fab54 and \greenD{(5,6)}(5,6)start color #1fab54, left parenthesis, 5, comma, 6, right parenthesis, end color #1fab54.
Are the lines parallel, perpendicular, or neither?

Given: abcd is a square. prove: ac ? bd. we are given that abcd is a square. if we consider triangle aeb and triangle aed, we see that side is congruent to side ad because sides of a square are congruent. we know that side ae is congruent to side ae by using the . finally, we know that side de is congruent to side because the diagonals of a square bisect each other. therefore, triangle aeb is congruent to triangle aed by congruency. we see that angle aed and angle aeb are a linear pair, and congruent by cpctc. thus, the measure of these angles will be 90°, and diagonal ac is perpendicular to diagonal bd by the .