batliwala wrote:

correct ans is E.

substituting values for x, y, and z and limiting conditions E. has the greatest value =4.

Well I agree with the answer E but I think the value of the expression in E will be +inf.

Here is how I thought of it:

2 *( x-z)*(x+z) + 2*y^2

To get the maximum value of this expression, we need to select the values as follws:

Maximum possible value of (x-z)

Maximum possible value of (x+z)

Maximum possible value of y

To get the Maximum possible value of (x-z):

Take the maximum possible value of x = 0

Take the minimum possible value of z = -2

Hence, maximum possible value of (x - z) = [0-(-2)] = 2

To get the Maximum possible value of (x+z):

Take the maximum possible value of x = 0

Take the maximum possible value of z = +inf

Hence, the maximum possible value of (x + z) = +inf

To get the Maximum possible value of y:

Take the maximum possible value of y = 1

So the maximum possible value of the given expression = 2 (2) (+inf) + 2(1) = +inf.

What am I missing?

Maximum possible value for x = 0

Minimum possible value for z = +inf