a ,

=> 3x + 9 + x -4 =0

=> 4x + 5 = 0

=> x = -5/4

b ).

=> \(\sqrt{\left(2x\right)^2+4x+1}+\sqrt{\left(x-3\right)^2}=0\)

=> \(\sqrt{\left(x+2\right)^2}+\sqrt{\left(x-3\right)^2}=0\)

=> \(\left(x+2\right)^2+\left(x-3\right)^2=0\)

=> x = -2 hoặc x = 3 

c ) .

=> \(\sqrt{x^2-2^2}+\sqrt{6-3x}=0\)

=> \(\sqrt{\left(x-2\right)\left(x+2\right)}+\sqrt{6-3x}=0\)

=> \(x^2-4+6-3x=0\)

=> \(x^2+2-3x=0\)

\(\Delta=\left(2\right)^2-4.1.-3=16\) > 0

=> pt có 2 nghiệm phân biệt

\(x_1=\dfrac{-2+\sqrt{16}}{2};x_2=\dfrac{-2-\sqrt{16}}{2}\)

b

đr

1 + 555 = 556

556 :  2 = 278 ( trang)

b ) . 

<=> \(x^2+4x+4=x^2-6x+9\)

=> \(x^2+4x+4-x^2+6x-9=0\)

=> \(10x-5=0\)

=> x = 5/10 = 1/2