First let us find the slope of the straight line formed when x1 = 0 to x2 = 2.5.
y = x^2 – 8
y1 = 0^2 – 8 = - 8
y2 = 2.5^2 – 8 = -1.75
The formula for finding the slope is:
m = (y2 – y1) / (x2 – x1)
m = (-1.75- (- 8)) / (2.5 – 0)
m = 2.5
The mean value theorem states that the slope must be 2.5 at least once between x1 = 0 to x2 = 2.5.
Taking the 1st derivative (slope) of the equation:
dy / dx = 2x
Since dy / dx = m = 2.5
2x = 2.5
x = 1.25
Therefore the answer is: One number at x = 1.25