Question 188963
 I assume the denominator is {{{a^2+2a-3}}}
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if so {{{a^2+2a-3}}}cannot =0 or equation would be undefined
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so set {{{a^2+2a-3=0}}}
:
{{{(a+3)(a-1)=0}}}
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so if a were -3 or 1 the equation would be undefined....therefore a=-3,1 are excluded values for a