數學(展開) 數學(展開)

1. (3-X)^2-X(X-1)
= 3^2-2(3)(X)+X^2-X^2+X
= 9-6X+X
= 9-5X

2. (X+4)(2X-7)-(X+4)(2X+7)
=(X+4)(2X-7-2X-7)
=(X+4)(-14)
=-14X-64

自己計先可以明白數學(展開)架!5明上網睇公式,睇到自己明白lau,然後就做下呢2題就會明白架啦!

1.(3-x)^2- x(x-1)
=[9-2(3)(x)+x^2]-x^2+1
=[9-6x+x^2]-x^2+1
=9-6x+x^2-x^2+1
=9-6x+1

2.(x+4)(2x-7)-(x+4)(2x+7)
=(2x^2-7x+8x-28)-(2x^2+7x+8x+28)
=2x^2-7x+8x-28-2x^2-7x-8x-28
=2x^2-2x^2-7x-7x+8x-8x-28-28
=-14x-56