3+[3a-2（a-1）]
=3+3a-2a+2
=a+5
（y^2-x^2）+（x^2+3y^2)
=y^2-x^2+x^2+3y^2
=4y^2
2ab-3b^2-(3ab-4b^2)=ab+b^2
①（-x+2x^2+5)+(4x^2-3-6x)
=-x+2x^2+5+4x^2-3-6x
=6x^2-7x+2
②(3a^2-ab+7)-(-4a^2+2ab+7）
=3a^2-ab+7+4a^2-2ab-7
=7a^2-3ab
（3x+1）+（2x^2+5x-1)-3x^2,其中x=10
（3x+1）+（2x^2+5x-1)-3x^2
=3x+1+2x^2+5x-1-3x^2
=-x^2+8x
当x=10时,
原式=-10^2+8*10=-20