Recover a Function from a Composition or Functional Equation
The question defines f via a composition identity like f((x−1)/(x+1)) = expression or a functional equation like f(x) − 6f(1/x) = expression, and asks to find f explicitly or evaluate it at a point.
When two constants $a , b$ satisfy $\lim _ { x \rightarrow 2 } \frac { x ^ { 2 } - ( a + 2 ) x + 2 a } { x ^ { 2 } - b } = 3$, what is the value of $a + b$? [2 points] (1) $- 6$ (2) $- 4$ (3) $- 2$ (4) 0 (5) 2
Consider the function $$f ( x ) = \begin{cases} - 3 x + a & ( x \leq 1 ) \\ \frac { x + b } { \sqrt { x + 3 } - 2 } & ( x > 1 ) \end{cases}$$ If $f ( x )$ is continuous on the entire set of real numbers, find the value of $a + b$. (Here, $a$ and $b$ are constants.) [4 points]
It is known that the function $f(x)$ is an odd function defined on $\mathbb{R}$. When $x \in (-\infty, 0)$, $f(x) = 2x^3 + x^2$. Then $f(2) = $ \_\_\_\_
Let $f : [-1,1] \rightarrow \mathbb{R}$ be a function such that $f\left(\sin\frac{x}{2}\right) = \sin x + \cos x$, for all $x \in [-\pi, \pi]$. The value of $f\left(\frac{3}{5}\right)$ is (A) $\frac{24}{25}$ (B) $\frac{31}{25}$ (C) $\frac{33}{25}$ (D) $\frac{7}{5}$.
If $g(x) = x^{2} + x - 2$ and $\frac{1}{2}\,g\circ f(x) = 2x^{2} - 5x + 2$, then $f(x)$ is equal to (1) $2x-3$ (2) $2x+3$ (3) $2x^{2}+3x+1$ (4) $2x^{2}-3x-1$
Let $f : R - \left\{ \frac { \alpha } { 6 } \right\} \rightarrow R$ be defined by $f ( x ) = \left( \frac { 5 x + 3 } { 6 x - \alpha } \right)$. Then the value of $\alpha$ for which $( f \circ f ) ( x ) = x$, for all $x \in R - \left\{ \frac { \alpha } { 6 } \right\}$, is (1) No such $\alpha$ exists (2) 5 (3) 8 (4) 6
Let $f : \mathbb { R } \rightarrow \mathbb { R }$ be a differentiable function that satisfies the relation $f ( x + y ) = f ( x ) + f ( y ) - 1 , \forall x , y \in \mathbb { R }$. If $f ^ { \prime } ( 0 ) = 2$, then $| f ( - 2 ) |$ is equal to
Let $f : \mathbb{R} - \{0\} \rightarrow \mathbb{R}$ be a function such that $f(x) - 6f\left(\frac{1}{x}\right) = \frac{35}{3x} - \frac{5}{2}$. If $\lim_{x \rightarrow 0}\left(\frac{1}{\alpha x} + f(x)\right) = \beta$; $\alpha, \beta \in \mathbb{R}$, then $\alpha + 2\beta$ is equal to (1) 5 (2) 3 (3) 4 (4) 6
Let $f : \mathbf { R } - \{ 0 \} \rightarrow ( - \infty , 1 )$ be a polynomial of degree 2, satisfying $f ( x ) f \left( \frac { 1 } { x } \right) = f ( x ) + f \left( \frac { 1 } { x } \right)$. If $f ( K ) = - 2 K$, then the sum of squares of all possible values of $K$ is : (1) 7 (2) 6 (3) 1 (4) 9
$$f ( 2 x + 5 ) = \tan \left( \frac { \pi } { 2 } x \right)$$ For the function $f$ given by the equality, what is the value $f ^ { -1 } ( 1 )$? A) $\frac { \pi } { 2 }$ B) $\frac { \pi } { 4 }$ C) $\pi$ D) $2 \pi$ E) $3 \pi$
Let $\mathrm { P } ( \mathrm { x } )$ be a second-degree polynomial and $\mathrm { Q } ( \mathrm { x } ) = \mathrm { k }$ be a constant polynomial such that $$\begin{aligned}
& P ( x ) + Q ( x ) = 2 x ^ { 2 } + 3 \\
& P ( Q ( x ) ) = 9
\end{aligned}$$ Accordingly, what is the sum of the values that k can take? A) $\frac { 1 } { 2 }$ B) $\frac { 1 } { 3 }$ C) $\frac { 2 } { 3 }$ D) $\frac { 1 } { 4 }$ E) $\frac { 3 } { 4 }$
For functions $f$ and $g$ defined on the set of positive real numbers $$\begin{aligned}
& ( f \circ g ) ( x ) = f ( x ) \cdot g ( x ) \\
& f ( x ) = 2 x + 3
\end{aligned}$$ Given that, what is the value of $\mathbf { g } ( \mathbf { 1 } )$? A) 1 B) 2 C) 3 D) 4 E) 5
Let $a$ and $b$ be non-zero real numbers. A function $f$ defined on the set of real numbers $$\begin{aligned}
& f ( a x + b ) = x \\
& f ( a ) = \frac { b } { a }
\end{aligned}$$ satisfies the equalities. Accordingly, what is the value of $\mathrm { f } ( 0 )$? A) $\frac { - 1 } { 2 }$ B) $\frac { - 1 } { 3 }$ C) $\frac { - 2 } { 3 }$ D) 1 E) 2
A function f defined on the set of real numbers satisfies the equality $$f ( x + y ) = f ( x ) + f ( y )$$ for every real numbers x and y. Given that $\mathbf { f } ( \mathbf { 2 } ) - \mathbf { f } ( \mathbf { 1 } ) = \mathbf { 1 0 }$, what is the result of the operation $$\frac { f ( 3 ) \cdot f ( 4 ) } { f ( 5 ) }$$? A) 15 B) 16 C) 18 D) 21 E) 24
Let $a$ and $b$ be non-zero integers. A function $f$ is defined on the set of real numbers as $$f ( x ) = a x + b$$ $$( f \circ f ) ( x ) = f ( x + 2 ) + f ( x )$$ According to this, what is the value of $f(3)$? A) 7 B) 8 C) 9 D) 10 E) 11
For functions $f$ and $g$ defined on the set of real numbers $$\begin{aligned}
& (f \circ g)(x) = x^2 + 3x + 1 \\
& (g \circ f)(x) = x^2 - x + 1
\end{aligned}$$ the equalities are satisfied. Given that $f(2) = 1$, what is the value of $f(3)$? A) 5 B) 6 C) 7 D) 8 E) 9