Question 72948
{{{(x-3)/((4x-5)*(x+1))}}}
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Just look at the denominator in the expression and recall that division by zero is never permitted.
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That being the case, you can't allow the denominator to be zero. But the denominator 
would become zero if either of the factors were equal to zero.
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The first factor would equal zero if:
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{{{4x - 5 = 0}}}
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Adding +5 to each side would result in:
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{{{4x = 5}}}
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and dividing both sides by 4 finally tells you that:
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{{{ x = 5/4}}}
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So if x = 5/4 the first factor in the denominator is zero, and this makes the entire 
denominator equal to zero. Since this is not permitted, you can't allow x to be {{{5/4}}}.
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On to the second factor in the denominator, namely {{{x + 1}}}. It also can't equal zero.
Set {{{x+1}}} equal to zero and solve for x.
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{{{x + 1 = 0}}}
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Subtract 1 from both sides and you get:
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{{{x = -1}}}
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That's all there is to it ... you cannot allow x to be {{{5/4}}} or {{{-1}}}. If you were
to graph the original expression, as the value of x began to approach either of these two
values, the value of y would explode upward or downward towards infinity ... the direction
depending on the sign and direction that the value of x was approaching from.
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Hope this helps you understand the process.