Q. Given the function f(x)=23x−x3, find f′(6). Express your answer as a single fraction in simplest radical form.Answer: f′(6)=
Find Derivative of Function: First, we need to find the derivative of the function f(x)=23x−x3. To do this, we will use the power rule for differentiation. The square root of x can be written as x1/2, so the function becomes f(x)=23x1/2−3x−1/2.
Differentiate First Term: Now, let's differentiate the first term (23)x(21). Using the power rule, the derivative of xn is n⋅x(n−1), so the derivative of (23)x(21) is (23)⋅(21)⋅x(21−1)=(43)x(−21).
Differentiate Second Term: Next, we differentiate the second term −3x−1/2. Again, using the power rule, the derivative of −3x−1/2 is −3∗(−1/2)∗x−1/2−1=(3/2)x−3/2.
Combine Derivatives: Combining the derivatives of both terms, we get the derivative of the function f(x), which is f′(x)=43x−21+23x−23.
Evaluate at x=6: Now we need to evaluate the derivative at x=6. Substituting x with 6, we get f′(6)=(43)(6)−21+(23)(6)−23.
Simplify Square Root and Cube Root: To simplify, we calculate the square root and the cube root of 6. The square root of 6 is 6, and the cube root of 6 is 63/2=(6)3. So, f′(6)=43(61)+23((6)31).
Find Common Denominator: We can simplify the expression further by finding a common denominator. The common denominator for 6 and (6)3 is (6)3. So, we multiply the first term by 66 to get the common denominator. f'(\(6) = \left(\frac{3}{4}\right)\left(\frac{\sqrt{6}}{\sqrt{6}}\right)\left(\frac{1}{\sqrt{6}}\right) + \left(\frac{3}{2}\right)\left(\frac{1}{(\sqrt{6})^3}\right) = \frac{3\sqrt{6}}{4\sqrt{6}^2} + \left(\frac{3}{2}\right)\left(\frac{1}{\sqrt{6}^3}\right).
Combine Terms with Common Denominator: Simplifying the denominators, we have 62=6 and 63=66. So, f′(6)=4⋅636+23(661)=2436+23(661).
Simplify Fraction: Now, we combine the terms over a common denominator, which is 246. To do this, we multiply the second term by 44 to get the common denominator. f′(6)=2436+23(2464)=2436+2466.
Factor Out 3 from Numerator: Adding the two fractions together, we get f′(6)=24636+6. This is the derivative of the function f(x) evaluated at x=6.
Factor Out 3 from Numerator: Adding the two fractions together, we get f′(6)=24636+6. This is the derivative of the function f(x) evaluated at x=6.Finally, we simplify the fraction by factoring out a 3 from the numerator. f′(6)=2463(6+2). We can simplify this further by dividing both the numerator and the denominator by 3. f′(6)=866+2.
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