Question 624720
<pre>
16a²-56xy+49b²

does not factor.  
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However if the xy had been ab, then

16a²-56ab+49b²

would have factored as

(4a-7b)(4a-7b)

(4x-7b)²

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30x³+25x²+5y

factors only by taking out common factor 5

5(6x³+5x²+y)

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However if the y had been an x

30x³+25x²+5x would become

5(6x³+5x²+1) which would become

5(3x+1)(2x+1)

These problems were designed to show you that you have to
be careful to look at the variables.

Edwin</pre>