Select the correct answer. Given: AB⟷⊥BC⟷ Prove: mAB⁢mBC=-1
Statements Reasons 1. AB⟷⊥BC⟷ given 2. mAB=d−01−0=d1=d mBC=e−01−0=e1=e application of the slope formula 3. draw the vertical line segment AC construction 4. ∠ABC is a right angle definition of perpendicular lines 5. △ABC is a right triangle definition of a right triangle 6. B⁢A=1+d2 B⁢C=e2+1 C⁢A=(d−e2)=d−e application of the distance formula 7. (1+d2)2+(e2+1)2=? Pythagorean theorem 8. (1+d2)+(e2+1)=d2−2⁢d⁢e+e22+d2+e2=d2−2⁢d⁢e+e22=-2⁢d⁢e-1=d⁢e simplify 9. -1=mAB⁢mBC substitution property of equality

Which expression is missing from step 7? A. (A+B)2 B. (d−e)2 C. -2⁢d⁢e D. A2+B2