To find y when x is known, go up or down from the x value to the graph, then across to the y-axis. To find x when y is known, go across from the y value to the graph, then down to the x-axis.
The graph crosses the y-axis where x = 0 and crosses the x-axis where y = 0. Reading graphs can also solve equations: the solution of 2x + 1 = 5 is the x-value where the line y = 2x + 1 meets the line y = 5.
Worked example
A line passes through (0, 3) and (2, 7). Where does it cross the y-axis?
- The y-axis is where x = 0.
- The point with x = 0 is (0, 3).
Answer:(0, 3)
Key words
- y-intercept
- where the graph crosses the y-axis
- x-intercept
- where the graph crosses the x-axis
- read off
- find a value from a graph
Practise this
New questions every time.
Common Core-referenced: HSF-IF.B.4