Hi Guys,

This problem from quadratic equations exercises that I am doing. Not sure how to proceed. Your help is much appreciated.

Prove that the expression is negative for all real values of x provided that k is greater than 64. Hence show that the expression is negative for all real values of y.

The first part I solved by completing the square to get . So -ve for .

Having trouble with the rest of the question. I tried simplifying but I end with an equation for order 4. What am I doing wrong?

Thanks for your help!