兩條數.......

1.26b-169-b²
= -(b²-26b+169)
= -(b-13)²
= -(b+13)(b-13)


2.25(3x-2y)²-9(2x+y)²
=[5(3x-2y)]² -[3(2x+y)]²
=[5(3x-2y)+3(2x+y)][5(3x-2y)+3(2x+y]
=[15x-10y+6x+3y][15x-10y-6x-3y]
=(21x+7y)(9x-13y)

1.26b-169-b²
= - ( - 26b+169+b²)
= - (169-26b-b²)
= - [(13-b)²]
= - (13-b)²


2.25(3x-2y)²-9(2x+y)²
=5²(3x-2y)²-3²(2x+y)²
=(15x-10y)²-(6x+3y)²
=[(15x-10y)+(6x+3y)] x [(15x-10y)-(6x+3y)]
=(15x-10y+6x+3y) x (15x-10y-6x-3y)
=(21x-7y)(9x-13y)
=189x+91y

*********我都唔知岩唔岩...你對一對答案

1. b=13