初二上300道数学题,越短越好,最好是计算题,
4个回答
(1)4a^3-(4a^3b^2)
=4a^3(1-b^2)
=4a^2(1+b(1-b)
(2)9x^2y^3-12xy^4+15xy^5
=3xy^3(3x-4y+5y^2)
(3)4(x-y)^3+(y^2)(y-x)^3
=4(x-y)^3-y^2(x-y)^3
=(x-y)^3(4-y^2)
=(x-y)^3(2-y)(2+y)
(4)(a+b)(a-b)-2b(3a-5b)
=a^2-b^2-6ab+10b^2
=a^2-6ab+9b^2
=(a-3b)^2
(5)(a-b)(3a+b)^2+(a+3b)^2(b-a)
=(a-b)(3a+b)^2-(a+3b)^2(a-b)
=(a-b)[(3a+b)^2-(a+3b)^2]
=(a-b)[(3a+b)+(a+3b)][(3a+b)-(a+3b)]
=(a-b)(4a+4b)(2a-2b)
=8(a+b)(a-b)^2
(6)(2x^2+1)^2-4(x^2+2x)^2
=(2x^2+1)^2-[2(x^2+2x)]^2
=(2x^2+1)^2-(2x^2+4x)^2
=[(2x^2+1)+(2x^2+4x)][(2x^2+1)-(2x^2+4x)]
=(4x^2+4x+1)(1-4x)
=(2x+1)^2(1-4x)
(7)(a+b)^2-2(a^2-b^2)+(a-b)^2
=[(a+b)^2-(a^2-b^2)]-[(a^2-b^2)-(a-b)^2]
=[(a+b)^2-(a+b)(a-b)]-[(a+b)(a-b)-(a-b)^2]
=(a+b)(a+b-a+b)-(a-b)(a+b-a+b)
=2b(a+b)-2b(a-b)
=2b(a+b-a+b)
=4b^2
(8)a^2-2ab+b^2-a+b
=(a-b)^2-(a-b)
=(a-b)(a-b-1)
