Решить уравнения: а)х квадрат-9х=0 в)3х квадрат+13х+14=0 б)5х квадрат-20=0 г)(х+5)квадрат+7(х+5)-8=0

Найдем корешки.

а) x - 9 * x = 0;

x * (x - 9) = 0;

x = 0;

x - 9 = 0;

x = 0;

x = 9.

в) 3 * х + 13 * x + 14 = 0;  

D = 13 - 4 * 3 * 14 = 169* - 12 * 14 = 169 - 168 = 1 = 1; 

x1 = (-13 + 1)/6 = -12/6 = -2; 

x2 = (-13 - 1)/6 = -14/6 = -7/3. 

б) 5 * х - 20 = 0; 

5 * (x - 4) = 0;

x - 4 = 0;

(x - 2) * (x + 2) = 0;

x - 2 = 0;

x + 2 = 0;

x = 2;

x = -2.

г) (х + 5) + 7 * (х + 5) - 8 = 0;  

x + 2 * 5 * x + 5 + 7 * x + 7 * 5 - 8 = 0; 

x + 10 * x + 25 + 7 * x + 35 - 8 = 0; 

x + 17 * x + 17 + 35 = 0; 

x + 17 * x + 52 = 0; 

D = 17 - 4 * 1 * 52 = 289 - 200 - 8 = 89 - 8 = 81 = 9; 

x1 = (-17 + 9)/2 = -8/2 = -4; 

x2 = (-17 - 9)/2 = -26/2 = -13.