-0,5x²+6x-7=0-x²-5x+6=05x²-8x-4=0Решить через дискриминант.

Решите задачу:

$1) -0,5 x^2 +6 x -7=0 \\a= -0,5; \ b=6; \ c=-7; \\D=b^2-4ac \\D= 36 = 6^2\\x_{1}=\frac{ -6-\sqrt{ 36 }}{ 2*-0,5 } = \frac{ -6-6 }{ -1 }= 12;\\\\x_{2}=\frac{ -6+\sqrt{ 36 }}{ 2*-0,5 } = \frac{ -6+6 }{ -1 }= 0;$

$2) -x^2 -5 x +6=0 \\a= -1; \ b=-5; \ c=+6; \\D=b^2-4ac \\D= 49 = 7^2\\x_{1}=\frac{ +5-\sqrt{ 49 }}{ 2*-1 } = \frac{ +5-7 }{ -2 }=1;\\\\x_{2}=\frac{ +5+\sqrt{ 49 }}{ 2*-1 } = \frac{ +5+7 }{ -2 }=-6;$

$3) 5 x^2 -8 x -4=0 \\a= 5; \ b=-8; \ c=-4; \\D=b^2-4ac \\D= 144 = 12^2\\x_{1}=\frac{ +8-\sqrt{ 144 }}{ 2*5 } = \frac{ +8-12 }{ 10 }=-0.4;\\\\x_{2}=\frac{ +8+\sqrt{ 144 }}{ 2*5 } = \frac{ +8+12 }{ 10 }=2;$