1. a ⊥ c, b ⊥ c
1. given
2. slope of c is x
2. given
3. slope of a is #&-\frac{1}{x}#&
3. slopes of ⊥ lines are negative reciprocals
4. slope of b is #&-\frac{1}{x}#&
4. slopes of ⊥ lines are negative reciprocals
5. slope of a = slope of b.
5. substitution property
6. a || b
6. parallel lines have equal slopes