Ответ:

1)n²-2×n×6-6²-n²+2²=n²-12n-36-n²+4=n²-n²-12n-36+4= -12n-32

2)

((2a)²+2×2a×1+1²-(a²-2×a×9-9²)=4a²+4a+1-a²+18a+81=4a²-a²+4a+18a+1+81=3a²+22a+82

3)

7x²-21x+x-3+20(x²-1²)=3(9x²-12x-4)+13=7x²-21x+x-3+20x²-

20=27x²-36x-12+13=7x²+20x²-27x²-21x+x+36x= -12+13+3+20=16x=24

x=24÷16

x=1,5

4)

(b²-25)(b²+25)-b⁴+81=b⁴-625-b⁴+81

(-¹/3)-(-1/3)-625+81=706