3(х+у)^3- 9ху (х+у)=3(x+y)(x^2-2xy+y^2)-9x^2y-9xy^2=3(x^3+x^2y-2x^2y-2xy^2+xy^2+y^3)-9x^2y+9xy^2=3x^3+3x^2y+6x^2y-6xy^2-3xy^2+3y^3-9x^2y+9xy^2=3x^3+3y^3=3х^3+3y^3=3(x^3+y^3)
150-6x в квадрате-90х/х(х+15)=0
X1=-25
X2=10
Во вложении
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36х³-х = х (36х² -1) = х ( (6х)² - 1²) = х (6х-1)(6х+1)