a * b = -40 (a)
a + b = -6 (b)
Solve (b) for (a)
a = -6-b
Replace on (a) and solve for b
-6-b * b = -40
-6b -b^2 = -40
-b^2-6b+40 = 0
apply quadratic equation:
![\frac{-b\pm\sqrt[]{b^2-4\cdot a\cdot C}}{2\cdot A}=\frac{6\pm\sqrt[]{36-4\cdot-1\cdot40}}{2\cdot-1}=(6\pm26)/(-2)](https://img.qammunity.org/2023/formulas/mathematics/college/qbfuhev048bzb7bcd8fht3ssja9iox8eo0.png)
positive : 6+26/-2 = 32/-2 = -16
negative = 6-26/-2 = 10
Use the negative:
10 * b = -40
b = -40 /-10
b= 4