-4х>28 | : -4
x < -7
При делении на отрицательное число знак неравенства меняется на противоположный.
X1 = -1; x2 = 3.
c =x1 * x2 = - 1 * 3 = - 3;
- b = x1 + x2 = - 1 + 3 = 2; b = - 2
x^2 + b*x + c = 0;
x^2 - 2 x - 3 = 0.
2) x1 = - 4;
x2 = 0;
c = x1 * x2 = - 4 * 0 = 0;
- b = x1 + x2 = - 4 + 0 = - 4; b = 4
x^2 + b* x + c = 0;
x^2 + 4x = 0
S=a+a+5+a+10+a+15=4a+30 км
Ответ: 4a+30 км
(x+y)/(x-y)+(x-y)/(x+y)=100
(x+y)²+(x-y)²=100(x-y)(x+y),x≠y U x≠-y
x²+2xy+y²+x²-2xy+y²=100(x²-y²)
2x²+2y²=100(x²-y²)
x²+y²=50(x²-y²)
подставим в 1
50(x²-y²)/(x²-y²)+(x²-y²)/50(x²-y²)=50+1/50=50,02