Step-by-step explanation:
[tex] \frac{5}{ {x }^{2} + 6x + 8} = \frac{a}{x + 2} + \frac{b}{x + 4} \\ factorizing \: the \: denominator \: of \: the \: first \: term \\ {x}^{2} + 6x + 8 \\ {x}^{2} + 4x + 2x + 8 \\ ( {x}^{2} + 4x)( + 2x + 8) \\ x(x + 4) + 2(x + 4) \\( x + 2)(x + 4) \\ \\ \\ \\ \frac{5}{(x + 2)(x + 4)} = \frac{a}{x + 2} + \frac{b}{x + 4 } \\ multiplying \: by \: the \: lcm = (x + 2)(x + 4) \\ 5 = a(x + 4) + b(x + 2) \\ put \: x = - 4 \\ 5 = a( - 4 + 4) + b( - 4 + 2) \\ 5 = a(0) + b( - 2) \\ 5 = 0 - 2b \\ 5 = - 2b \\ b = \frac{5}{ - 2} \\ b = - 2 \ \frac{1}{2} \\ substituting \: b = - 2 \frac{1}{2} and \: put \: x = - 2 \\ 5 = a( - 2 + 4) + b( - 2 + 2) \\ 5 = a(2) + b(0) \\ 5 = 2a \\ a = 2 \frac{1}{2} \\ a + b = 2 \frac{1}{2} + ( - 2 \frac{1}{2} ) \\ 2 \frac{1}{2} - 2 \frac{1}{2} \\ a + b = 0[/tex]
