-9x²-30xy-25y² = - 1*(9x²+30xy+25y²) = -1*(3х+5у)

при x= -2 ; y= 1.5

-1*( 3*(-2) +5 * 1,5) = -1*( - 6+ 7,5) = - 1*1,5 = - 1,5