A-5b)(a+5b)-4(a+5b)=(a+5b)(a-5b-4)
1.=(a^2-x^2)(<span>a^2+x^2)=a^4-x^4
2.=</span>(4x^2-1)<span>(4x^2+1)=16x^4-1
3.=x^2-4xy^2+4y^4-x^2-4xy^2-4y^4=-8xy^2
</span>4.=(9-x^4)<span>(9+x^4)=81-x^8
</span>5.=(4x^2+y^2)<span>(4x^2-y^2)=16x^4-y^4
</span>6.= (9a^4+4b^4)<span> (9a^4-4b^4)=81a^8-16b^8</span><span>
</span>
2) 5а^3 - 15а^2b + 20ab^2 = 5a (a^2 - 3ab + 4b^2)
4) -3xy^2 - 15x^2y - 21x^2y^2 = -3xy (y + 5x + 7xy)
6) -6ax^2 + 9x^2 - 12x^4 - 3a^2x^2 = -3x^2 (2a - 3 + 4x^2 + а^2)
(2х-у)+(у-х)-у= 2х-у+у-х-у=х-у