理想去闯
幼苗
共回答了20个问题采纳率:100% 举报
1.(x-3)(x+2)-(x+3)2
=x2-x-6-(x2+6x+9)
= x2-x-6-x2-6x-9
= -7x-15
2.(x+1)2-(x-2)(x+2
)=x2+2x+1-(x2-4)
=2x+5
3.(a-2b)(a-3b)+(a-2b)2-(a-3b)2
=(a-3b)[(a-2b)-(a-3b)]+(a-2b)2
=b(a-3b) +(a-2b)2
=ab-3b2+a2-4ab+4b2
=a2-3ab+b2
4.2(a+1)2-(2a-3)(2a+3)
=2a2+4a+2-4a2+9
= -2a2+4a+11
5.(x+1/2)2+(x-1/2)2
=x2+x+1/4+x2-x+1/4
=2x2+1/2
6.(1/3a-3/4b)2-(1/3a+3/4b)2
=a2/9-ab/2+9b2/16-( a2/9+ab/2+9b2/16)
= -ab
7.(x-2)(x+2)(x2+4)
=(x2-4)( x2+4)
=x4-16
8.(a+1)(a-1)(a2-1)
=(a2-1) (a2-1)
=a4-2a2+1
9.(x+3y)2+2(x-y)(x+y)+(x-3y)2
=x2+6xy+9y2+2x2-2y2+ x2-6xy+9y2
=4x2+16y2
10.[(a-1/2)2+(a+1/2)2](2a2-1/2)
=(a2-a+1/4+ a2+a+1/4) (2a2-1/2)
=(2a2+1/2) (2a2-1/2)
=4a4-1/4
利用完全平方公式:
99.82=(100-0.2)2=1002-2×100×0.2+0.22=10000-40+0.04=9960.04
20052=(2000+5)2=20002+2×2000×5+52=4000000+20000+25=4020025
填空:
1.x2+ 6xy +9y2=(x+3y)2
2.a2+ 4x2-32xy+64y2-4a2 1/4=(x-4y)2
3.x2-8xy+ 16y2 =(x-4y)2
4.(x+b)2- x2+2xb-a2+2ab =(a-b)2
第2和4道题目是不是有误?
1年前
7