Question

Решите уравнение: (x+21)/(x2-9) = x/(x+3)

Answer 1

(X+21)/((X+3)(X-3)=X/(X+3)     ДОМНОЖАЕМ НА (X-3)

X+21=X(X-3)

X+21=X^2-3X

X+21-X^2+3X=0

X^-4X-21=0

ПО ВИЕТА

 X1+X2=4

X1*X2=-21

X1=7

X2=-3

 

Answer 2

(х+21)/(х-3)(х+3)=х(х-3)/(х-3)(х+3)

х+21=х^2-3x

x^2-4x-21=0

D=4^2-4*1*(-21)=16+84=100=10^2

x1=4+10/2=7      x2=4-10/2=-3