Question

Where does the graph of y=2x2-x-3 cross as the x-axis?

Answer 1

This can be determined by finding the x-intercept. In doing so, we let y=0 to find the value of x.

y= 2x^2 -x -3
[0 = 2x^2 -x-3]÷2
0 = x^2 -1/2 x - 3/2

Complete the squares:

1/16 + 3/2 = x^2 - 1/2x + 1/16
25/16 = (x -1/4)^2
sqrt (25/16) = x - 1/4
+/- 5/4 = x - 1/4

Thus,
x = 1/4 + 5/4 = 3/2
x = 1/4 - 5/4 = -1

Thus, the graph crosses at x = 3/2 and x = -1.