一大堆中二數學唔識(expend)

1.
(-12-20m)(3-5m)
=-12(3-5m)-20m(3-5m)
=-36+60m-60m+60m²
=-36+60m²

2.
(4m+n)(8m-2n)
=4m(8m-2n)+n(8m-2n)
=32m²-8mn+8mn-2n²
=32m²-2n²

3.
咩是2m2次-9

4.
2(3x-4)(3x+4/2)
=(6x-8)(3x+4/2)
=6x(3x+4/2)-4(3x+4/2)
=3x(3x+4)-2(3x+4)
=9x²+12x-6x-8
=9x²+6x-8

5.
4(7x+2)(7x-2/2)
=(28x+8)(7x-2/2)
=28x(7x-2/2)+8(7x-2/2)
=14x²-28x+4(7x-2)
=14x²-28x+28x-8
=14x²-8

6.
=x²(8-5x)(8+5x)
=(8x²-5x³)(8+5x)
=8x²(8+5x)-5x³(8+5x)
=64x²+40x³-40x³+25x4次
=64x²+25x4次

比意見算
1.(-3-5m)抽-出黎 跟住(a+b)(a-b)
2.直接(a+b)(a-b)
3.(-9n-2m^2)抽- 又(a+b)(a-b)
4.有d唔明
可能係先用6約左入面d over 2同3
再(a+b)(a-b)
5.同4
6.同4