Question

tìm x biết 

a)    (x+2)^2=81

b)    5^x+5^c+2=650

c)   (x+1)^x+7=(x+1)x+3

Answer 1

a,\(\left(x+2\right)^2=81>0\)

\(\orbr{\begin{cases}\left(x+2\right)^2=9^2\\\left(x+2\right)^2=\left(-9\right)^2\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x+2=9\\x+2=-9\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=7\\x=-11\end{cases}}\)

Answer 2

a)\(\left(x+2\right)^2=81\\ =>\left(x+2\right)=9^2hay\left(x+2\right)=\left(-9\right)^2\)

x+2=9                     x+2=-9

x=9-2                      x=-9-2

x=7(TM)                  x=-11(TM)

        Vậy x=7 hay x=-9