Factor polynomial $$ -27u^{3}+125 $$

$$ -27u^{3}+125 = ( -3u+5 )( 9u^{2}+15u+25 ) $$

Step 1 :

To factor $ -27u^{3}+125 $ we can use difference of cubes formula:

$$ I^3 - II^3 = (I - II)(I^2 + I \cdot II + II^2) $$

After putting $ I = 5 $ and $ II = 3u $ , we have:

$$ -27u^{3}+125 = ( -3u+5 ) ( 9u^{2}+15u+25 ) $$

Step 2 :

Step 2: Identify constants $ a $ , $ b $ and $ c $.
$ a $ is a number in front of the $ x^2 $ term $ b $ is a number in front of the $ x $ term and $ c $ is a constant. In this case:

$$ a = 9 , b = 15 ~ \text{ and } ~ c = 25 $$

Step 3: Multiply the leading coefficient $\color{blue}{ a = 9 }$ by the constant term $\color{blue}{c = 25} $.

$$ a \cdot c = 225 $$

Step 4: Find out two numbers that multiply to $ a \cdot c = 225 $ and add to $ b = 15 $.

Step 5: All pairs of numbers with a product of $ 225 $ are:

PRODUCT = 225
1     225	-1     -225
3     75	-3     -75
5     45	-5     -45
9     25	-9     -25
15     15	-15     -15

Step 6: Find out which factor pair sums up to $\color{blue}{ b = 15 }$

Step 7: Because none of these pairs will give us a sum of $ \color{blue}{ 15 }$, we conclude the polynomial cannot be factored.

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