（a+2b+3c）(a-2b+3c)
=[(a+3c)+2b][(a+3c)-2b]
=(a+3c)²-(2b)²
=a²+6ac+9c²-4b²
(x+2)的平方-(x-3)(x+2)
=(x+2)(x+2-x+3)
=5(x+2)
=5x+10
(3x+2)(3x-2)-4x(x-1)-(2x--1)的的平方-（x-1)(x+2) ,其中x=-五分之三
(3x+2)(3x-2)-4x(x-1)-(2x--1)的的平方-（x-1)(x+2)
=9x²-4-4x²+4x-4x²+4x-1-x²-x+2
=7x-3
=-21/5-3
=-36/5