Vertical and horizontal lines have equations that are simpler than all other lines!
Vertical lines have equations of the form ‘$\,x = \text{some number}\,$’.
Horizontal lines have equations of the form ‘$\,y = \text{some number}\,$’.
Why?
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Since they're commonly mixed up, two memory devices are offered, so you'll always get them right.
The points $\,(x,y)\,$ that satisfy the equation $\,x = 3\,$
(that is, $\,x + 0y = 3\,$) 
Memory Device for Vertical Lines 
The points $\,(x,y)\,$ that satisfy the equation $\,y = 3\,$
(that is, $\,0x + y = 3\,$) 
Memory Device for Horizontal Lines 
CONCEPT QUESTIONS EXERCISE:
On this exercise, you will not key in your answer.However, you can check to see if your answer is correct. 
PROBLEM TYPES:
