WHat is a quick mathod of determine wheter a quadratic form is positive definite, postive semidefinite etc

Question

caozeyuan · Answer

Google pretty much just give a general theory, there is no way to quickly calculate, I know the definitions of them already

caozeyuan · Answer

My girlfriend has a homework question saying that determine the quartic form x^t*A*x where A is the matix( 2,3    is p.d. or p.sd, or n.d or n.sd or indefinite
                                 3, 8)

caozeyuan · Answer

so the Q form comes out as 2x1^2+6x1x2+8x2^2

caozeyuan · Answer

nvm, I got it