Answer:
Slope is positive for all x, so always increasing
Step-by-step explanation:
Increasing/decreasing depends on the slope of the function, which is f'
f'(x) = 9x² + 18x + 25
If f'(x) > 0 for all x, then his claim is correct (increasing for all x)
If there's even 1 x-value for which f'(x) is not positive, his claim is incorrect
f'(x) is a quadratic function.
9x² + 18x + 25
9(x² + 2x) + 25
9(x² + 2(x)(1) + 1² - 1²) + 25
9(x + 1)² - 9 + 25
9(x + 1)² + 16
Since the minimum value of f' is 16, it's always positive.
Hence, the claim is correct
