Final answer:
A vertical line is the type of line used in hair design to make a hairstyle appear longer and narrower.
Step-by-step explanation:
The type of line used to create length and height in hair design, making the hair style appear longer and narrower, is a vertical line. Vertical lines have the effect of elongating and slimming the appearance of the hair style, similar to how they create the impression of stability and height in architectural contexts, like classical building columns or tree trunks. This is because vertical lines draw the eye upward, creating an illusion of increased length and reduced width. The type of line used to create length and height in hair design while making the hair style appear longer and narrower is a vertical line. Vertical lines suggest stability and can create the illusion of height and length. In hair design, vertical lines are often used to make the hair style appear longer and narrower.