A line with a positive slope and a line with a negative slope or perpendicular

Answer 1

Slope of a line

m = (y₂-y₁)/(x₂-x₁)

According to this formula, there are 4 possible scenarios:

(y₂-y₁) is + and (x₂-x₁) is + | this means that the slope is +

(y₂-y₁) is + and (x₂-x₁) is - | this means that the slope is -

(y₂-y₁) is - and (x₂-x₁) is + | this means that the slope is -

(y₂-y₁) is - and (x₂-x₁) is - | this means that the slope is +

Slope of a parallel line

If the 2 lines are parallel, that means that they have the same slope

m₁ = m₂

Slope of a perpendicular line

If the 2 lines are perpendicular, then the slopes are "negative reciprocal" of one another. In other words:

m₁ * m₂ = -1

Example: if m₁ = 3/4, then m₂ = - 4/3

Hope this helps