Determine as expressões designatórias das funções derivadas
Funções seno, co-seno e tangente: Infinito 12 A - Parte 3 Pág. 50 Ex. 23
- Determine as expressões designatórias das funções derivadas das funções:
a) $f:x \to \operatorname{sen} (3x) + \cos x$
b) $g:x \to {\cos ^2}(2x)$
c) $h:\alpha \to \frac{{1 – \cos (3\alpha )}}{\alpha }$
d) $i:z \to \frac{{1 – \cos (2z)}}{{1 + \cos (2z)}}$
e) $j:t \to \cos \left( {4 – 3t} \right)$
- Sabendo que as funções $f$ e $g$ são deriváveis e que $g(1) = 3$, $g'(1) = 2$ e $f'(3) = 5$, determine, nos pontos indicados, o valor da derivada das funções seguintes:
a) $f\left( {g(x)} \right)$ para $x = 1$;
b) $f\left( {g\left( {2x + 1} \right)} \right)$ para $x = 0$.
- a)
$$\begin{array}{*{20}{l}}
{f'(x)}& = &{\left( {\operatorname{sen} (3x) + \cos x} \right)’} \\
{}& = &{\cos (3x) \times \left( {3x} \right)’ – \operatorname{sen} x} \\
{}& = &{3\cos (3x) – \operatorname{sen} x}
\end{array}$$
b)
$$\begin{array}{*{20}{l}}
{g'(x)}& = &{\left( {{{\cos }^2}(2x)} \right)’} \\
{}& = &{2 \times \cos (2x) \times \left( {\cos (2x)} \right)’} \\
{}& = &{2\cos (2x) \times \left( { – \operatorname{sen} (2x) \times \left( {2x} \right)’} \right)} \\
{}& = &{ – 2\left( {2\cos (2x) \times \operatorname{sen} (2x)} \right)} \\
{}& = &{ – 2\operatorname{sen} (4x)}
\end{array}$$
c)
\[\begin{array}{*{20}{l}}
{h’\left( \alpha \right)}& = &{{{\left( {\frac{{1 – \cos (3\alpha )}}{\alpha }} \right)}^\prime }} \\
{}& = &{\frac{{\operatorname{sen} (3\alpha ) \times {{\left( {3\alpha } \right)}^\prime } \times \alpha – 1 \times \left( {1 – \cos (3\alpha )} \right)}}{{{\alpha ^2}}}} \\
{}& = &{\begin{array}{*{20}{l}}
{\frac{{3\alpha \operatorname{sen} (3\alpha ) – 1 + \cos (3\alpha )}}{{{\alpha ^2}}},}&{\alpha \ne 0}
\end{array}}
\end{array}\]
d)
\[\begin{array}{*{20}{l}}
{i’\left( z \right)}& = &{{{\left( {\frac{{1 – \cos (2z)}}{{1 + \cos (2z)}}} \right)}^\prime }} \\
{}& = &{\frac{{\operatorname{sen} (2z) \times {{\left( {2z} \right)}^\prime } \times \left( {1 + \cos (2z)} \right) + \operatorname{sen} (2z) \times {{\left( {2z} \right)}^\prime } \times \left( {1 – \cos (2z)} \right)}}{{{{\left( {1 + \cos (2z)} \right)}^2}}}} \\
{}& = &{\frac{{2\operatorname{sen} (2z) + 2\operatorname{sen} (2z)\cos (2z) + 2\operatorname{sen} (2z) – 2\operatorname{sen} (2z)\cos (2z)}}{{{{\left( {1 + \cos (2z)} \right)}^2}}}} \\
{}& = &{\begin{array}{*{20}{l}}
{\frac{{4\operatorname{sen} (2z)}}{{{{\left( {1 + \cos (2z)} \right)}^2}}},}&{\alpha \ne \frac{\pi }{2} + k\pi ,k \in \mathbb{Z}}
\end{array}}
\end{array}\]
e)
$$\begin{array}{*{20}{l}}
{j'(t)}& = &{\left( {\cos \left( {4 – 3t} \right)} \right)’} \\
{}& = &{ – \operatorname{sen} \left( {4 – 3t} \right) \times \left( {4 – 3t} \right)’} \\
{}& = &{3\operatorname{sen} \left( {4 – 3t} \right)}
\end{array}$$
- a)
\[\begin{array}{*{20}{l}}
{{{\left( {f\left( {g(x)} \right)} \right)}^\prime }\left( 1 \right)}& = &{f’\left( {g\left( 1 \right)} \right) \times g’\left( 1 \right)} \\
{}& = &{f’\left( 3 \right) \times 2} \\
{}& = &{5 \times 2} \\
{}& = &{10}
\end{array}\]
b)
\[\begin{array}{*{20}{l}}
{{{\left( {f\left( {g\left( {2x + 1} \right)} \right)} \right)}^\prime }\left( 0 \right)}& = &{f’\left( {g\left( {2 \times 0 + 1} \right)} \right) \times g’\left( {2 \times 0 + 1} \right) \times {{\left( {2x + 1} \right)}^\prime }} \\
{}& = &{f’\left( {g\left( 1 \right)} \right) \times g’\left( 1 \right) \times 2} \\
{}& = &{f’\left( 3 \right) \times 2 \times 2} \\
{}& = &{5 \times 2 \times 2} \\
{}& = &{20}
\end{array}\]
Se $f’$ e $g’$ existem e se $f \circ g$ está definida, então $$\left( {f \circ g} \right)'(x) = f’\left( {g(x)} \right) \times g'(x)$$





