Writing linear equations, step by step
Writing y = mx + b is the skill that turns points into a line.
The question
Write the equation of the line through (1, −7) and (3, −15).
Write the equation of the line through (1, −7) and (3, −15)
slope = (−15 − (−7)) ÷ (3 − 1)
−8 ÷ 2=−4
b = −7 − (−4)(1)=−3
y = −4x − 3
- Find the slope first: rise over run, (−15 − (−7)) ÷ (3 − 1) = −4.
- Put a point back in to find b: b = y − mx = −7 − (−4)(1) = −3.
- Write it as y = mx + b: y = −4x − 3.
How it works.
- 01
Find the slope first: rise over run, (−15 − (−7)) ÷ (3 − 1) = −4.
- 02
Put a point back in to find b: b = y − mx = −7 − (−4)(1) = −3.
- 03
Write it as y = mx + b: y = −4x − 3.