Hello I have a small problem and I am wondering if someone could help me with Cayley Hamilton Theorem..please!

Let D = [4 0 0, 0 -1 0, 0 0 9]. Find a matrix D^1/2 E M(3x3) (C) such that

D^1/2 * D^1/2 = D...

I know we have to use this product....

A = VDV^-1....and A^k = VD^kv-1....for example A^2 = VD^2V^-1...

But I cant take the square root of the D and its elements because it contains -1 as one of its elements...

please help me!

thanks a lot!