1.先化简,再求值[（a-1/2）²-（a+1/2）²]（a+3）,其中a=-2 2.若a+b=5,ab=6,求a^4+b^4,a^8+b^8的值 3.已知a(a-1)-(a²-b)=4,求(a²+b²)/2-ab的值 正确必满意,蟹蟹~

1.先化简,再求值[（a-1/2）²-（a+1/2）²]（a+3）,其中a=-2 2.若a+b=5,ab=6,求a^4+b^4,a^8+b^8的值 3.已知a(a-1)-(a²-b)=4,求(a²+b²)/2-ab的值 正确必满意,蟹蟹~
1.先化简,再求值[（a-1/2）²-（a+1/2）²]（a+3）,其中a=-2 2.若a+b=5,ab=6,求a^4+b^4,a^8+b^8的值 3.已知a(a-1)-(a²-b)=4,求(a²+b²)/2-ab的值 正确必满意,蟹蟹~

1.先化简,再求值[（a-1/2）²-（a+1/2）²]（a+3）,其中a=-2 2.若a+b=5,ab=6,求a^4+b^4,a^8+b^8的值 3.已知a(a-1)-(a²-b)=4,求(a²+b²)/2-ab的值 正确必满意,蟹蟹~
[(a-1/2)^2-(a+1/2)^2](a+3)
=[(a-1/2+a+1/2)(a-1/2-a-1/2)](a+3)
=[2ax(-1/4)](a+3)
=-a/2(a+3)
当a=-2
-a/2(a+3)
=-2/2(-2+3)
=-1x1
=-1

[(a-1/2)^2-(a+1/2)^2](a+3)
=[(a-1/2+a+1/2)(a-1/2-a-1/2)](a+3)
=[2ax(-1/4)](a+3)
=-a/2(a+3)
当a=-2
-a/2(a+3)
=-2/2(-2+3)
=-1x1
=-1