X2−7x−18=0
D= b^{2} -4ac=b2−4ac=
=(-7)^{2} -4*1*(-18)=(−7)2−4∗1∗(−18)=
=49+72=121.
x_{1} = \frac{ -b- \sqrt{D} }{2a} = \frac{7-11}{2} =-2x1=2a−b−√D=27−11=−2
x_{2} =\frac{ -b+\sqrt{D} }{2a}= \frac{7+11}{2} =9x2=2a−b+√D=27+11=9
Ответ:9