Answer
LCD=(x+1)(x+3)(x+7)
Work Step by Step
$\frac{4}{x^{2}+4x+3}$, $\frac{4x-2}{x^{2}+10x+21}$
$x^{2}$+4x+3=$x^{2}$+x+3x+3=x(x+1)+3(x+1)=(x+3)(x+1)
$x^{2}$+10x+21=$x^{2}$+7x+3x+21=x(x+7)+3(x+7)=(x+3)(x+7)
LCD=(x+1)(x+3)(x+7)
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