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D( x )
((5*x^4*y^2)/7)*z <= 0
((5*x^4*y^2)/7)*z <= 0
((5*x^4*y^2)/7)*z <= 0
((5*x^4*y^2)/7)*z = 0
5/7*x^4*y^2*z = 0 // : 5/7*y^2*z
x^4 = 0
x = 0
x <= 0
(-oo:0) (0:+oo) x - +
x in (0:+oo)
ln(((5*x^4*y^2)/7)*z) = 0
ln(((5*x^4*y^2)/7)*z) = ln(e^0)
((5*x^4*y^2)/7)*z = e^0
((5*x^4*y^2)/7)*z-e^0 = 0
5/7*x^4*y^2*z = 1 // : 5/7*y^2*z
x^4 = 7/5*y^-2*z^-1
x^4 = 7/5*y^-2*z^-1 // ^ 1/4
abs(x) = (7/5)^(1/4)*y^(-1/2)*z^(-1/4)
x = (7/5)^(1/4)*y^(-1/2)*z^(-1/4) or x = -((7/5)^(1/4)*y^(-1/2)*z^(-1/4))
x in { (7/5)^(1/4)*y^(-1/2)*z^(-1/4), -((7/5)^(1/4)*y^(-1/2)*z^(-1/4)) }
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