( Х + y )*( X - y ) - ( x^2 + 3y^2 ) = x^2 - y^2 - x^2 - 3y^2 = - 4y^2
Х^2 - 5 = а
а^2 - 3а - 4 = 0
D = 9 + 16 = 25 = 5^2
a1 = ( 3 + 5 ) : 2 = 4
a2 = ( 3 - 5 ) : 2 = - 1
X^2 - 5 = 4
X^2 = 9
X1,2 = + ; - 3
X^2 - 5 = - 1
X^2 = 4
X1,2 = + ; - 2
Ответ 2 ; 3 ; - 2 ; - 3
[(3x+7)²-(3x-7)²]/x=(3x+7-3x+7)(3x+7+3x-7)/x=14*6x/x=84