Răspuns:
[tex]a \: x {}^{2} + 3 {}^{2} = 5 {}^{2} \\ {x}^{2} + 9 = 25 \\ {x}^{2} = 25 - 9 \\ {x}^{2} = 16 \\ x = 4 \: sau \: - 4 \\ c. \:13 + 2x {}^{2} = {x}^{2} - 12 \\ {2x}^{2} = {x}^{2} - 12 - 13 \\ {2x}^{2} = {x}^{2} - 25 \\ {x}^{2} = - 25 \\ x = multimea \: vida [/tex]
[tex]d. \: x \times(2x - 6) = 2 \times (4 - 3x - {x}^{2}) \\ 2x {}^{2} - 6x = 8 - 6x - 2x {}^{2} \\ 2x {}^{2} = 8 - 6x - 2x {}^{2} + 6x \\ - 8 = - 2x {}^{2} - 2x {}^{2} \\ - 8 = - 4x {}^{2} \\ 2 = {x}^{2} \\ x = \sqrt{2} [/tex]
