Tìm \[x\] biết: (a) 4x(x−3)−4x^2+1=9

a) \[4x\left( {x - 3} \right) - 4{x^2} + 1 = 9\]

\[4{x^2} - 12x - 4{x^2} + 1 = 9\]

\[ - 12x = 8\]

\[x = \frac{{ - 2}}{3}\]

Vậy \[x = \frac{{ - 2}}{3}\]

b) \[\left( {2x - 5} \right)\left( {3x + 4} \right) - 6x\left( {x - 3} \right) = 5x\].

\[6{x^2} + 8x - 15x - 20 - 6{x^2} + 18x = 5x\]

\[11x - 20 = 5x\]

\[6x = 20\]

\[x = \frac{{10}}{3}\]

Vậy \[x = \frac{{10}}{3}\]

c) \[{\left( {x + 3} \right)^2} + {\left( {x - 7} \right)^2} = x\left( {2x - 5} \right)\].

\[{x^2} + 6x + 9 + {x^2} - 14x + 49 = 2{x^2} - 5x\]

\[3x = 58\]

\[x = \frac{{58}}{3}\]

Vậy\[x = \frac{{58}}{3}\].