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Multiple Choice
Over which interval is the graph of increasing?
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Verified step by step guidance
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Step 1: To determine where the graph of f(x) is increasing, calculate the derivative of f(x). The derivative, f'(x), represents the slope of the tangent line to the graph of f(x). For f(x) = (1/2)x^2 + 5x + 6, use the power rule to find f'(x). The derivative is f'(x) = x + 5.
Step 2: Set f'(x) = 0 to find the critical points. Solving x + 5 = 0 gives x = -5. This is the critical point where the slope of the tangent line is zero.
Step 3: Determine the intervals where f'(x) is positive (increasing) or negative (decreasing). To do this, test values of x in the intervals divided by the critical point (-∞, -5) and (-5, ∞). For example, test x = -6 and x = 0 in f'(x).
Step 4: Evaluate f'(x) for the test values. If f'(x) > 0, the graph is increasing; if f'(x) < 0, the graph is decreasing. For x = -6, f'(-6) = -6 + 5 = -1 (negative, decreasing). For x = 0, f'(0) = 0 + 5 = 5 (positive, increasing).
Step 5: Based on the sign of f'(x), conclude that the graph of f(x) is decreasing on the interval (-∞, -5) and increasing on the interval (-5, ∞). The correct answer is (-5, ∞).