To analyze the joint PDF \( f_{X,Y}(x,y) \) given by
\[ f_{X,Y}(x,y) = \begin{cases} cxy & \text{if } 0 \leq x \leq y \leq 1 \ 0 & \text{otherwise} \end{cases} \]
we first need to determine the normalizing constant \( c \) and the support of the random variables \( X \) and \( Y \) defined in this joint PDF.
a) Evaluating \( f_{X|Y}(2 | 0.5) \)
- Understanding the condition: The conditional PDF \( f_{X|Y}(x|y) \) is only defined when the joint PDF \( f_{X,Y}(x,y) \) is non-zero.
- Conditions for \( y = 0.5 \): For \( Y = 0.5 \), we look at the joint PDF: We need to find \( x \) such that \( 0 \leq x \leq 0.5 \leq 1 \). However, when we consider \( x = 2 \), we see that \( 2 \) does not satisfy the condition \( 0 \leq x \leq 0.5 \).
- Result: Therefore, since \( x = 2 \) is not in the support for \( Y = 0.5 \), we conclude that
\[ f_{X|Y}(2|0.5) = 0 \]
Thus, the statement in part (a) is true.
b) Evaluating \( f_{X|Y}(0.5 | 2) \)
- Understanding the condition: As before, we must consider the support of \( Y \).
- Conditions for \( y = 2 \): The condition states that \( 0 \leq x \leq y \leq 1 \). However, \( y = 2 \) does not satisfy \( y \leq 1 \) since 2 is outside this range.
- Result: Therefore, since \( y = 2 \) is outside the valid support for the joint PDF, we conclude that
\[ f_{X|Y}(0.5|2) = 0 \]
Thus, the statement in part (b) is also true.
Conclusion
- a) True: \( f_{X|Y}(2 | 0.5) = 0 \)
- b) True: \( f_{X|Y}(0.5 | 2) = 0 \)