3/7+(-9/14)= -3/14
-5/9-1/12= -23/26
-2/3*5/8= -5/12
3/28:(-5/7)= -3/20
3 3/9 * 3 1/5 + 3 1/5 * 1 5/12 = 3 1/5 * (3 3/9 + 1 5/12) = 3 1/5 (3 12/36 + 1 15/36) = 3 1/5 * 4 27/36 = 3 1/5 * 4 3/4 = 16/5 * 19/4 = 76/5 = 15 1/5
Х^2-5х=14
Х^2-5х-14=0
D=b^2-4ac
D=25+56=81
√81=9
<span>Х1=(-b+ √D):2а</span>
<span>Х2=(-b-√D):2а</span>
Х1=(5+9):2=7
Х2=(5-9):2=-2
Ответ: 7.