Question

(x+3)(x-5)(x+2)(x-4)=60

Answer 1

-4x=60|÷(-4)
x=-15
Ответ: -15

Answer 2

(x+3)(x-5)(x+2)(x-4)=60
$( x^{2} -5x+3x-15)*( x^{2} -4x+2x-8)=60 \ ( x^{2} -2x-15)*( x^{2} -2x-8)=60$
Пусть $x^{2} -2x-15= alpha$. Тогда 
$alpha ( alpha +7)=60 \ alpha^{2} +7 alpha -60=0 \ alpha_{1} =-12; alpha _{2} =5 \ \ x^{2} -2x-15=-12 \ x^{2} -2x-3=0 \ x_{1} =-1; x_{2}=3 \ \ x^{2} -2x-15=5 \ x^{2} -2x-20=0 \ x_{1}=1- sqrt{21}; x_{2}=1+ sqrt{21}$