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Derivative of a sum of exponential, power, and logarithmic terms

Let f(x)=2ex+3x2−ln⁡(x)f(x) = 2e^x + 3x^2 - \ln(x). Find f′(x)f'(x).

Hint

Differentiate each term separately using the constant multiple rule and the sum/difference rule. Recall that ddx[ex]=ex\frac{d}{dx}[e^x] = e^x, ddx[xn]=nxn−1\frac{d}{dx}[x^n] = nx^{n-1}, and ddx[ln⁡x]=1x\frac{d}{dx}[\ln x] = \frac{1}{x}.

Step-by-step solution

Apply the sum/difference rule to differentiate term by term: f′(x)=ddx[2ex]+ddx[3x2]−ddx[ln⁡x]f'(x) = \frac{d}{dx}[2e^x] + \frac{d}{dx}[3x^2] - \frac{d}{dx}[\ln x]. This breaks the problem into three simpler derivatives, each handled with a known rule.

Using the constant multiple rule, ddx[2ex]=2ex\frac{d}{dx}[2e^x] = 2e^x and ddx[3x2]=3⋅2x=6x\frac{d}{dx}[3x^2] = 3\cdot 2x = 6x by the power rule, while ddx[ln⁡x]=1x\frac{d}{dx}[\ln x] = \frac{1}{x}. Combining these gives f′(x)=2ex+6x−1xf'(x) = 2e^x + 6x - \frac{1}{x}.

Sign of the derivative term from the logarithm

In the derivative f′(x)=2ex+6x−1xf'(x) = 2e^x + 6x - \frac{1}{x}, is the term from the logarithm added or subtracted?

Hint

Consider the difference rule: when you differentiate a term that is being subtracted, the minus sign is preserved in the derivative.

Step-by-step solution

The term coming from the logarithm is subtracted. Since the original function subtracts the natural logarithm term, the difference rule keeps that minus sign when differentiating. This gives the negative one over x term in the final derivative.

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