1.8x-2(5-3x)
=8x-10+6x
=14x-10
2.-2(x-3)-3(2x-5)
=-2x+6-6x+15
=-8x+21
3.已知A=x的2次方 +xy+y的2次方,B=-3xy-x的2次方 ,求2A-3B
2A-3B
=2(x^2+xy+y)-3(-3xy-x^2)
=2x^2+2xy+2y+9xy+3x^2
=5x^2+11xy+2y
(^是乘方的数学符号)
4.先化简,再求值：2x的2次方-（x的2次方-5x)-(3x的2次方+2）,其中x=2分之1
(2x)^2-(x^2-5x)-[(3x)^2+2]
=4x^2-x^2+5x-9x^2-2
=-6x^2+5x-2
=-6(1/4)+5(1/2)-2
=-3/2+5/2-2
=1-2
=-1