Question

What IS the slope of a line that is perpendicular to the line y= --x + 5?

• -2
-1/2
1/2
• 2

Answer 1

Slopes of perpendicular lines.

Let k: y = a₁x + b₁ and l: y = a₂x + b₂. Then

k ║ l ⇔ a₁ = a₂

k ⊥ l ⇔ a₁ · a₂ = -1

We have the line y = -x + 5 ⇒ a₁ = -1.

Therefore

a₂ · (-1) = -1

-a₂ = -1 Ichange the signs

a₂ = 1