a. 
is a joint density function if its integral over the given support is 1:
so the answer is yes.
b. We should first find the density of the marginal distribution, 
:
Then
or about 0.2019.
For the other probability, we can use the joint PDF directly:
which is about 0.7326.
c. We already know the PDF for 
, so we just integrate:
![E[Y]=\displaystyle\int_{-\infty}^\infty y\,f_Y(y)\,\mathrm dy=\frac15\int_0^\infty ye^{-y/5}\,\mathrm dy=\boxed5](https://tex.z-dn.net/?f=E%5BY%5D%3D%5Cdisplaystyle%5Cint_%7B-%5Cinfty%7D%5E%5Cinfty%20y%5C%2Cf_Y%28y%29%5C%2C%5Cmathrm%20dy%3D%5Cfrac15%5Cint_0%5E%5Cinfty%20ye%5E%7B-y%2F5%7D%5C%2C%5Cmathrm%20dy%3D%5Cboxed5)
The answer to the question
Answer:
Step-by-step explanation:
We can determine if the triangle is a right triangle by using the Pythagorean theorem
a^2 +b^2 = c^2 where a and b are the legs and c is the hypotenuse
25^2 + 27^2 = 48^2
625+729=2304
1354 ≠2304
This is not true, so this is not a right triangle
The answer would be D. y=-2x+8
