4.
а) (2-3n)²-9n⁴=(2-3n)²-(3n²)²=(2-3n-3n²)(2-3n+3n²)
б) (a-5)²+2(a-5)+1=(a-5+1)²=(a-4)²
в) x⁶-x⁴-x²+1=x⁴(x²-1)-(x²-1)=(x⁴-1)(x²-1)
г) 8b³-1/27=(2b)³-(1/3)³=(2b-1/3)(4b²+2b/3+1/9)
5. (87²-13²)/(91²-34*91+17²)=(87-13)(87+13)/(91-17)²=74*100/74²=100/74=1/0.74
6. (x-3)²+(3-x)(x+3)=(x+2)²-x²
(x-3)²+9-x²=x²+4x+4-x²
x²-6x+9+9-x²=4x+4
18-6x=4x+4
10x=14
x=1.4