1.计算：
(1)(2a+3b) (2a-b)
=4a^2-2ab+6ab-3b^2
=4a^2+4ab-3b^2
(2) 5x^2 (x+1)(x-1)
=5x^2 (x^2-1)
=5x^4-5x^2
(3) (2x+y-1)^2
=(2x+y)^2-2(2x+y)+1
=4x^2+4xy+y^2-4x-2y+1
2.计算：
(1) (2a)^3·b^4 ÷12a^3 b^2
= 8a^3·b^4 ÷12a^3 b^2
=2/3b^2
(2) (-2/3a^7 b^5) ÷ 3/2 a^2 b^5
=(-2/3)÷ 3/2*(a^7 b^5÷ a^2 b^5)
=-4/9a^5
(3)(6/5 a^3 x^4-0.9ax^3)÷3/5ax^3
=(6/5 a^3 x^4-9/10ax^3)÷3/5ax^3
=3/5ax^3(2a^2 x-3/2)÷3/5ax^3
=2a^2 x-3/2
(4) (7x^2 y^3-8x^3 y^2 z)÷8x^2 y^2
= 8x^2 y^2(7/8y-xz)÷8x^2 y^2
= 7/8y-xz
3.分解因式
(1) 25x^2 -16y^2
=(5x+4y)(5x-4y)
(2) (a-b)(x-y)-(b-a)(x+y)
=(a-b)(x-y)+(a-b)(x+y)
=(a-b)(x-y+x+y)
=2x(a-b)