(√(7) + 1)^2 - 2 √(7)

(7+2×√7×1+1)-2√7= 8+2√7-2√7=8

(√(7) + 1)^2 - 2 √(7)  = (√7+1)^2 - 2√7 = 7 + 2√7 + 1 - 2√7 = 7 + 1 = 8.

z^3+3z=-7z^2-21=

=z(3+z^2)=-7(3+z^2)=

=(z-7)(3+z^2)

120*х=нск(х,120)*нсд(х,120)

120*х=600*60

2х=600

х=300

ответ: 300