Split 20 into two non negative numbers x; y such that the product of x and y^2 is a maximum

Degrees of freedom rules tell that the number of unknowns should be equal to the number of equations involved in the system of equations. The numerical or algebraic expressions of the two given statements are represented by the equations: 

(1)  20  = x+y
(2) P = x y^2 

where x and y are the unknowns and P is the product and the maximum. 

When finding for the maximum, we take the first derivative of the function and equate to zero. we can substitute x by the equation in (1). Hence, 
P = xy^2 = (20-y)y^2 = 20y^2 - y^3
P' = 40 y -  3y^2 = 0
getting y,
40y = 3y^2
40 = 3y
y = 40/3
x= 56/3
The two numbers then are fractions 40/3 and 56/3. 

Okay so for every triangle has three angles that always add up to 180 degrees. and to tell the difference between whether they are secure, right or obtuse is that acute: has one angle that is less than 90 degrees. right triangle means there is at least one angle that is exactly 90 degrees. and an obtuse angle has an angle that is bigger than 180 degrees. i’ll do #13 as an example: 13. 40 and 50 so if every triangle has 180 degrees 40+50= 90 degrees then180-90= 90 degrees so the third angle is 90 degrees and because this triangle has a 90 degree angle it means it is a right triangle

You have to give us options