Math 1 · Unit 3 · Lesson 4 · part 4 of 6
The other crossing: the x-intercept
b is where the line crosses the y-axis, the y-intercept, the value when x is 0.
The other crossing: the x-intercept
b is where the line crosses the y-axis, the y-intercept, the value when x is 0. There is a second crossing: the x-intercept, where the line crosses the x-axis, the value of x when y is 0. To find it, put y = 0 into the equation and solve for x.
Find both intercepts of y = 2x − 6
y-intercept: put x = 0. y = 2 × 0 − 6 = −6. The point (0, −6).
x-intercept: put y = 0. 0 = 2x − 6. Add 6 to both sides: 6 = 2x. Multiply by 12: x = 3. The point (3, 0).
What they mean in a story
A tank starts with 60 gallons and drains 4 gallons a minute: y = −4x + 60. The y-intercept (0, 60) is the starting amount. The x-intercept is when y = 0: 0 = −4x + 60, so x = 15. At 15 minutes the tank is empty. The x-intercept is when the story reaches zero.