神武运镖成就奇遇:初二数学题目帮助

因式分解
1.x*x+3xy-2x-6y
=x(x+3y)-2(x+3y)
=(x-2)(x+3y)
2.4a-1+b*b-4a*a
=b*b-4a*a+4a-1
=b*b-4(a*a-a+1/4)
=b*b-4(a-1/2)(a-1/2)
=[b+2(a-1/2)][b-2(a-1/2)]
=(b+2a-1)(b-2a+1)

解答题
X+Y=3.........1
2X-Y>1........2
由1得 X=3-Y..........3
Y=3-X..........4
将3代入2 2(3-Y)-Y>1 将4代入2 2X-(3-X)>1
6-2Y-Y>1 2X-3+X>1
6-3Y>1 3X-3>1
-3Y>-5 3X>4
Y<5/3 X>4/3
所以，X>4/3,Y<5/3

1\ =x^2-2x+3xy-6y
=x(x-2)+3y(x-2)
=(x+3y)(x-2)
2\ =4a-4a^2-1+b^2
=4a(1-a)-(1-b)(1+b)

3\ y<5/3 x>4/3

X(X-2)-3Y(X-2)
=(X-3Y)(X-2)

-4a·a+4a-1+b·b
=-(2A-1)^2+B^2
=(B+2A-1)(B-2A+1)

X+Y=3
2X-Y>1 所以 Y<2X-1

把Y =3-X带入 推出3-X<2X-1 推出X>3/4

所以 y<5/3 x>4/3

希望你看得明