1.
(x-3y)(x+3y)=x²-9y²
2.
(a-2)(a+2)+4=a²-4+4=a²
3.
49-9x²=(7-3x)(7+3x)
4.
-64+25y²=(5y-8)(5y+8)
5.
(2a-5b)(2a+5b)+(6b-3a)(6b+3a)=4a²-25b²+36b²-9a²=11b²-5a²
6.
(6x-1)(6x+1)-4x(9x+3)=-4
36x²-1-36x²-12x=-4
12x=3/:12
x=1/4
x=0,25
7.
54²-16²=(54-16)(54+16)=38*70=2660