Given: AB ⟷ ⊥ BC ⟷ Prove: m AB ⁢ m BC = - 1 A perpendicular line of x-axis and y-axis has red line A (1, d) and blue line C (1, e) with all crossing the origin B (0, 0) Statements Reasons 1. AB ⟷ ⊥ BC ⟷ given 2. m AB = d − 0 1 − 0 = d 1 = d m BC = e − 0 1 − 0 = e 1 = e application of the slope formula 3. draw the vertical line segment AC construction 4. ∠ ABC is a right angle definition of a right angle 5. △ ABC is a right triangle definition of a right triangle 6. B ⁢ A = 1 + d 2 B ⁢ C = e 2 + 1 C ⁢ A = ( d − e 2 ) = d − e application of the distance formula 7. ( 1 + d 2 ) 2 + ( e 2 + 1 ) 2 = ( d − e ) 2 Pythagorean theorem 8. ( 1 + d 2 ) + ( e 2 + 1 ) = d 2 − 2 ⁢ d ⁢ e + e 2 2 + d 2 + e 2 = d 2 − 2 ⁢ d ⁢ e + e 2 2 = - 2 ⁢ d ⁢ e - 1 = d ⁢ e simplify 9. - 1 = m AB ⁢ m BC substitution property of equality Which step of the proof contains an error? A. Step 2 B. Step 8 C. Step 4 D. Step 6