Matrix A=

5k 1

9 1

calculate (transpose(x)*A*x ) where x=

x1

x2

find the set of values for k where (transpose(x)*A*x ) > 0 for all non zero x in R^2

I am having real difficulty on this one, as when i did this calculation i got:

5kx1^2 + 10x1x2 + x2^2

Now it says for non-zero x but that means they can still be negative? Please help.