64 х^2+ 1/х^2 =
= (8 х)^2+ (1/х)^2 =
= (8 х)^2+ 2*(8х)*(1/х) +
(1/х)^2 - 2*(8х)*(1/х) =
= (8 х+ 1/х)^2 - 2*8 =
= (8 х+ 1/х)^2 - 16 =
65
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(8 х+ 1/х)^2 - 16 = 65
(8 х+ 1/х)^2 = 16 + 65 = 81 = 9^2 = (-9)^2
(8 х+ 1/х) =9 или -9
Решение Вашего задания во вложении
2х - (х+3у)/6 + (х-2у)/3 = 2х*6-(х+3у)+2*(х-2у) = 12х-х-3у+2х-4у = 13х-7у
X-x/2<7+1
x/2<8
x<16
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