F.1.數學

(2-X)^2 - (3X+1)^2

= (2-X)(2-X) - (3X+1)(3X+1)

=( 4-2X-2X+X^2 ) -( 9X^2+3X+3X+1)
[ (2-X)(2-X) : 2x2=4, 2x(-X)=-2X, -Xx2=-2X, -X x -X=X^2
(3X+1)(3x-1) : 3Xx3X=9X^2, 3Xx1=3X , 1x3X=3X , 1x1=1]

=4-2X-2X+X^2-9X^2-3X-3X-1
[-( 9X^2+3X+3X+1)=-9X^2-3X-3X-1(拆括號,"負"乘入去)]

= -8X^2-10X+3
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(2-x)^2-(3x+1)^2
= (4-4x+x^2)-(9x^2+6x+1)
= 4-4x+x^2-9x^2-6x-1
= -8x^2-10x+3