Sunday, December 31, 2017

Calculus and Its Applications, Chapter 1, 1.6, Section 1.6, Problem 26

Differentiate $F(x) = (-3x^2 +4x)( 7 \sqrt{x} + 1)$
By multiplying first before differentiating we get

$
\begin{equation}
\begin{aligned}
F(x) &= \left( -3x^2 + 4x \right) \left( 7x^{\frac{1}{2}} + 1 \right)\\
\\
F(x) &= -21x^{\frac{5}{2}} - 3x^2 + 28x^{\frac{3}{2}} + 4x
\end{aligned}
\end{equation}
$


Thus,

$
\begin{equation}
\begin{aligned}
F'(x) &= \frac{d}{dx} \left( -21x^{\frac{5}{2}} - 3x^2 + 28x^{\frac{3}{2}} + 4x \right)\\
\\
&= -21 \cdot \frac{d}{dx} \left( x^{\frac{5}{2}} \right) - 3 \cdot \frac{d}{dx} (x^2) + 28 \cdot \frac{d}{dx} \left( x^{\frac{3}{2}} \right) + 4 \cdot
\frac{d}{dx} (x)\\
\\
&= -21 \cdot \frac{5}{2} \left( x^{\frac{5}{2} - 1} \right) -3 \cdot 2 \left( x^{2 - 1} \right) + 28 \cdot \frac{3}{2} \left( x^{\frac{3}{2} - 1} \right)
+ 4 \cdot (1)\\
\\
&= \frac{-105}{2} x^{\frac{3}{2}} - 6x + 42x^{\frac{1}{2}} + 4\\
\\
&= \frac{-105}{2} \sqrt{x^3} - 6x + 42 \sqrt{x} + 4
\end{aligned}
\end{equation}
$

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