多项式的因式分解1.(x²+3)²-4x²2.-x²+1/43.-4(x+2y)²+9(2x-y)²4.简便计算：9*1

1.(x²+3)²-4x²
=(x²+2x+3)(x²-2x+3)
2.-x²+1/4
=1/4-x²
=(1/2+x)(1/2-x)
3.-4(x+2y)²+9(2x-y)²
=9(2x-y)²-4(x+2y)²
=(6x-3y+2x+4y)(6x-3y-2x-4y)
=(8x+y)(4x-7y)
4.简便计算：9*1.2²-16*1.4²
=(3×1.2)²-(4×1.4)²
=(3.6+5.6)(3.6-5.6)
=-2×9.2
=-18.4
5.计算：（1-1/2²）（1-1/3²）（1-1/4²）······（1-1/10²）
=(1-1/2)(1+1/2)(1-1/3)(1+1/3)(1-1/4)(1+1/4)……(1-1/10)(1+1/10)
=1/2 × 3/2×2/3 × 4/3×3/4 × …… ×10/9×9/10 ×11/10
=1/2×11/10
=11/20

(x²+3)²-4x²
=(x²+3+2x)(x²+3-2x)

(x²+3)²-4x²=(x²+3-2x)(x²+3+2x)
-x²+1/4=-(x-1/2)(x+1/2)
-4(x+2y)²+9(2x-y)²={3(2x-y)+2(x+2y)}{3(2x-y)-2(x+2y)}=(8x+y)(4x-7y)
9*1.2²-16*1.4²=...