1) (5-а)²=5²-2*5а+а²=25-10а+а²
2) (4x)²+2+4х*1+1²=16x²+8x+1
3) (3a-7)(3a+7)= (3a)²-7²=9a²-49
4) (a-8)(a-7)-(a-9)²=a²-7a-8a+56-(a²-18a+81)=a²-7a-8a+56-a²+18a-81=3a-25
5) 4b*(b+1)-(2b-1)²=4b²+4b-(4b²-4b+1)=4b²+4b-4b²+4b-1=8b-1
6) x(x-5)+(3x+1)²=x²-5x+9x²+6x+1=10x²+x+1
7) c²-49=(c-7)(c+7)
8) 25a²-4b²=(5a-2b)(5a+2b)
9)a²-2ay+y²=(a-y)²
10)16y-y³=y(16-y²)=y(4-y)(4+y)
11)(2x-5)²-2(7x-1)²=4x²-20x+25-2(49x²-14x+1)=4x²-20x+25-98x²+28x-2=-94x²+8x+23
12)798²+4*798+4=798²+3196=640000
13)(3x-2)²-(3x-1)(3x+1)=-2x
9x²-12x+4-(9x²-1)=-2x
9x²-12x+4-9x²+1=-2x
-12x+5=-2x
-12x+2x=-5
-10x=-5
x=5/10
x=1/2=0.5