5x的2次方y-3xy的2次方-7(x的2次方y-7分之2xy)

问题描述:

5x的2次方y-3xy的2次方-7(x的2次方y-7分之2xy)

原式=5x^2y-3xy^2-7x^2y+2xy
=(5-7)x^2y-3xy^2+2xy
=-2x^2y-3xy^2+2xy