Problem: The vertex of the parabola y=x2−8x+c will be a point on the x-axis if the value of c is:
Answer Choices:
A. −16
B. −4
C. 4
D. 8
E. 16
Solution:
y=x2−8x+C=x2−8x+16+C−16=(x−4)2+C−16 (a parabola). For its vertex to be on the x-axis, its coordinates must be (4,0) so that C must have the value 16 .