1．A的平方减去B的平方加上B减去4分之一,要用初一的因式分解,2．4（X的平方加上Y）（X平方减去Y）减去（2X的平方减去Y）平方其中X＝2Y＝—5先化简,在求值,这里面的括号,就是题中的括号,我急用

(1)a²-b²+b-1/4==A²-(B²-B+1/4)
=A²-(B-1/2)²
=(A+B-1/2)(A-B+1/2）
（2）=4（x²＋y）(x²-y)-(2x²-y)²
= 4x^4-4y²-(2x²-y)²
=(2x²)²-(2x²-y)²-4y²
=(2x²+2x²-y)(2x²-2x²+y)-4y²
=(4x²-y)y-4y²
=y(4x²-5y)
=-5×(16+25)
=-205

1)a^2-b^2+b-1/4
=a^2-(b^2-b+1/4)
=a^2-(b-1/2)^2
=(a+b-1/2)(a-b+1/2)
完全平方公式
2）4（x^2+y）(x^2-y)-(2x^2-y)^2
=4(x^4-y^2)-(4x^4-4x^2y+y^2)
=-4y^2+4x^2y-y^2
=4x^2y-5y^2
=100*(-5/2)-25/4
=-250-25/4
=-1025/4

A²-B²+B-1/4
=A²-(B²-B+1/4)
=A²-(B-1/2)²
=(A+B-1/2)(A-B+1/2)
4(X²+Y)(X²-Y)-(2X²-Y)²
=4(X^4-Y²)-(4X^4-4X²Y+Y²)
=4X^4-4Y²-4X^4+4X²Y-Y²
=4X²Y-5Y²
=4*4*(-5)-5*25
=-205

1.A2-B2+B-1/4=A2-(B2-B+1/4)=A2-(B-1/2)2=(A+B-1/2)(A-B+1/2)
2.4(X2+Y)(X2-Y)-(2X2-Y)2=4(X4-Y2)-(4X4-4X2*Y+Y2)=-5Y2+4X2*Y
代入数值算一下就好咯