1. D=1-(4*(-56)) = 225
X1= -(1+√(225))/2=-8
X2 =-(1-√(225))/2 = 7
или
2. По теореме Виета
x1+x2 = -b/a = -1/1= -1
x1*x2 = c/a = -56/1 = -56
X1=-8
X2 = 7
((Х+6):х)+(4х:(х+6))=4
1+6/х)+(4+2/3х)=4
1+4-4=6/х+2/3х
1=8/4х
1=8:4х
8:4х=1
4х=1-8
4х=-7
х=-7:4
х=-1 2/7 ( минус одна целая,две седьмых)
4a-1; a =2x+3
4(2x+3)-1=8x+12-1=8x+11