ツответ............................
X²+7x-18=0
D=7²+4*18=49+72=121=11²
x(1)=(-7+11)/2=4/2=2
x(2)=(-7-11)/2=-9
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
А) 4*a²-3*a+13
б)21*x⁵-3*x⁹