(3/2x^2-5xy+y^2)-[-3xy+2(1/4x^2-xy)+2/3y^2],其中x=1,y=-2 化简求值

题目

(3/2x^2-5xy+y^2)-[-3xy+2(1/4x^2-xy)+2/3y^2],其中x=1,y=-2 化简求值

答案

(2分之3x的2次方-5xy+y的2次方)-【-3xy+2(4分之一x的2次方-xy)+3分之2y的2次方】
=3/2x²-5xy+y²-(-3xy+1/2x²-2xy+2/3y²)
=3/2x²-5xy+y²+5xy-1/2x²-2/3y²
=x²-1/3y²