Question

Giải các phương trình sau

a) 2x+5 = 20 - 3x

b)\(4x^2+5x=0\)

c)\(\left(x-2\right)^2=1-5x\)

d)\(x^2+5x+6=0\)

e)\(x^4-5x^2+4=0\)

f)\(5\left(x^2-3x\right)=\left(4x+2\right)^2+1\)

Answer 1

a, <=> 5x= 15 <=> x=5

b, <=> x(4x+5)=0 <=> \(\left[{}\begin{matrix}x=0\\x=-\frac{5}{4}\end{matrix}\right.\)

c, <=> \(x^2-4x+4=1-5x< =>x^2+x+3=0< =>\)vô nghiệm

d, <=>(x+2)(x+3)=0<=> \(\left[{}\begin{matrix}x=-2\\x=-3\end{matrix}\right.\)

e, Đặt x^2=a(đk a>=0)

Pt<=>\(a^2-5a+4=0< =>\left(a-4\right)\left(a-1\right)=0< =>\left[{}\begin{matrix}a=4\left(TM\right)< =>x=2\\a=1\left(TM\right)< =>x=1\end{matrix}\right.\)

f, <=>\(5x^2-15x=16x^2+16x+4+1< =>11x^2+31x+5=0< =>\left[{}\begin{matrix}x=\frac{-31+\sqrt{741}}{22}\\x=\frac{-31-\sqrt{741}}{22}\end{matrix}\right.\)