Equations that Describe a Line
CONCEPTS
Equations
• Standard form: ax + by = c
• Slope intercept form: y = mx + b
• Point–Slope Form: y – y₁ = m (x – x₁), given point (x₁, y₁)
Tips
• Standard form is the standard equation used when doing word problems.
• Slope intercept form is used to determine the slope & y – intercept
• Point–Slope Form is used when one has the slope & 1 point (or 2 points if you calculate the slope from the 2 points) and an equation needs to be created.
PRACTICE PROBLEMS
Question 1 Put 9x – y – 5=0 in slope intercept form
-- Answer -- y = 9x – 5
Question 2 What is the equation of the line for the line the in the graph below?
-- Answer -- 3/2 x
Slope = (0 - -3) / (2 – 0) = 3/2, y-intercept = 0
y = mx + b => y = 3/2 x + 0 = 3/2 x
Question 3 Which is an equation that passes through (4,3) & (9,2)?
-- Answer -- y = –1/5x + 19/5
m = –1/5, y = –1/5x + 19/5
ACT PRACTICE PROBLEMS
