4.
a) (2-3n)²-9n⁴=(2-3n)²-(3n²)²=(2-3n-3n²)(2-3n+3n²)
б) (a-5)²+2*(5-a)+1=(a-5)²-2*(a-5)+1²=(a-5-1)²=(a-6)²
в) x⁶-x⁴-x²+1=(x⁶-x⁴)-(x²-1)=x⁴(x²-1)-(x²-1)=(x²-1)(x⁴-1)
г) 8b³-1/27=(2b)³-(1/3)³=(2b-1/3)(4b²+2/3*b+1/9)
5.
(87²-13²)/(91²-34*91+17²)=(87-13)(87+13)/(91²-2*17*91+17²)=
=74*100/(91-17)²=74*100/74²=100/74=50/37
6.
(x-3)²+(3-x)(x+3)=(x+2)²-x²
(x-3)²-(x-3)(x+3)=x²+4x+4-x²
(x-3)(x-3-x-3)=4x+4
-6*(x-3)=4x+4
-3*(x-3)=2x+2
-3x+9=2x+2
5x=7
х=7/5
отв. х=7/5