Asked by silly_muffin
                The random variables X and Y are distributed according to the joint PDF:
It has the value of a*x^2 if 1 <= x <= 2 and 0 <= y <= x, and 0 otherwise. What's the value of the constant a?
            
        It has the value of a*x^2 if 1 <= x <= 2 and 0 <= y <= x, and 0 otherwise. What's the value of the constant a?
Answers
                    Answered by
            silly_muffin
            
    Could you repeat that calculation and see if 2^4 is 8 or 16?
    
                    Answered by
            Bot
            
    To find the value of the constant a, we need to use the condition that the joint probability density function integrates to one over the entire domain of X and Y. 
The domain of X is from 1 to 2, and the domain of Y is from 0 to X. Therefore, we can write:
∫∫ f(x,y) dx dy = 1, where the integral is taken over the region D in the xy-plane defined by D={(x,y): 1<=x<=2, 0<=y<=x}
Substituting the given PDF, we get:
∫∫ a*x^2 dx dy = 1
Integrating with respect to y first, we get:
∫1^x a*x^2 dy = a*x^3/3
Substituting the limits of y, we get:
∫∫ a*x^2 dx dy = ∫1^2 (a*x^3/3) dx
Integrating with respect to x, we get:
∫1^2 (a*x^3/3) dx = a/3 * [(2^4)/4 - (1^4)/4] = a/3 * (8/4 - 1/4) = a/3 * 7/4
Therefore, we have:
a/3 * 7/4 = 1
Multiplying both sides by 12/7, we get:
a = 36/7
Hence, the value of the constant a is 36/7.
    
The domain of X is from 1 to 2, and the domain of Y is from 0 to X. Therefore, we can write:
∫∫ f(x,y) dx dy = 1, where the integral is taken over the region D in the xy-plane defined by D={(x,y): 1<=x<=2, 0<=y<=x}
Substituting the given PDF, we get:
∫∫ a*x^2 dx dy = 1
Integrating with respect to y first, we get:
∫1^x a*x^2 dy = a*x^3/3
Substituting the limits of y, we get:
∫∫ a*x^2 dx dy = ∫1^2 (a*x^3/3) dx
Integrating with respect to x, we get:
∫1^2 (a*x^3/3) dx = a/3 * [(2^4)/4 - (1^4)/4] = a/3 * (8/4 - 1/4) = a/3 * 7/4
Therefore, we have:
a/3 * 7/4 = 1
Multiplying both sides by 12/7, we get:
a = 36/7
Hence, the value of the constant a is 36/7.
                    Answered by
            Bot
            
    You are correct - 2^4 is 16, not 8. Therefore, the correct calculation is:
∫1^2 (a*x^3/3) dx = a/3 * [(2^4)/4 - (1^4)/4] = a/3 * (16/4 - 1/4) = a/3 * 15/4
Therefore, we have:
a/3 * 15/4 = 1
Multiplying both sides by 12/15, we get:
a = 4/5
Hence, the value of the constant a is 4/5.
    
∫1^2 (a*x^3/3) dx = a/3 * [(2^4)/4 - (1^4)/4] = a/3 * (16/4 - 1/4) = a/3 * 15/4
Therefore, we have:
a/3 * 15/4 = 1
Multiplying both sides by 12/15, we get:
a = 4/5
Hence, the value of the constant a is 4/5.
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