Question

1.计算(x+3y)^2-(2x+y)(x-y)

Answer 1

(x+3y)^2-(2x+y)(x-y)

=x²+6xy+9y²-(2x²-2xy+xy-y²)

=x²+6xy+9y²-2x²+xy+y²

=-x²+7xy+10y²

(x+2)(x-2)-4x(x-1)+(2x+1)^2

=x²-4-4x²+4x+4x²+4x+1

=x²+8x-3

当x=-½时

原式=（-1/2)²+8×(-1/2)-3

=¼-4-3

=-6.75