4. a^2+2ab+b^2–2ab+a^2–b^2=a•2a
2a^2 = a•2a
a•2a = a•2a
5. x^3+2x^2–4x–8=0
(х+2)•(х^2–4)=0
х+2=0; х^2–4=0
х1=–2; х^2=4
х2=2; х3=–2
4. a^2–2ab+b^2–2ab+2a^2–b^2 =
= a(3a–4b)
3a^2–4ab = a(3a–4b)
a(3a–4b) = a(3a–4b)
5. 2x^3+x^2–8x–4=0
(2x+1)(x^2–4)=0
2x+1=0; х^2–4=0
2x=–1; х^2=4
x1=–1/2 х2=2; х3=–2