Question

Tìm x biết:
a)4x+4x²-2(2x²+4x+1)=0
b)x²+2x+5=0
c)x³+3x²+3x=7
d)x+2=(x+2)²

^???

Answer 1

a: \(4x+4x^2-2\left(2x^2+4x+1\right)=0\)

=>\(4x^2+4x-4x^2-8x-2=0\)

=>\(-4x=2\)

=>\(x=-\dfrac{2}{4}=-\dfrac{1}{2}\)

b: \(x^2+2x+5=0\)

=>\(x^2+2x+1+4=0\)

=>\(\left(x+1\right)^2+4=0\)(vô lý)

c: \(x^3+3x^2+3x=7\)

=>\(x^3+3x^2+3x+1=8\)

=>\(\left(x+1\right)^3=2^3\)

=>x+1=2

=>x=2-1=1

d: \(\left(x+2\right)^2=x+2\)

=>\(\left(x+2\right)^2-\left(x+2\right)=0\)

=>\(\left(x+2\right)\left(x+2-1\right)=0\)

=>(x+2)(x+1)=0

=>\(\left[{}\begin{matrix}x+2=0\\x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=-1\end{matrix}\right.\)