If `y=cos x` ,then what is the maximum value of `y`

If x+y =12 what is the maximum value of xy?

If x+y=20 and P=xy, then what is the maximum value of P?

There are two numbers x and y such that the sum of two times x and three times y is less than or equal to 360. If the value os x is greater than or equal to 160, then what is the maximum value of y ?

If x+y=3 then show that the maximum value of x^(2) y is 4.

If 3cos x+4cos y=5, then the maximum value of 3sin x+4sin y is

If 1 le x le 3 and 2 le y le 4 , what is the maximum value of ((x)/(y)) ?

If x+y=52 and x-y=20 , then what is the value of x:y ?