Question 474995
<pre>  4x<sup>3</sup> +  x<sup>2</sup> + 17x - 15 : -x<sup>2</sup> - x - 5</pre>We will call the first expression "dividend" and the second "divisor".
First thing to do is to look at the first term of both expressions,
4x<sup>3</sup> and -x<sup>2</sup>, and answer the question 
"How much is (4x<sup>3</sup>)/(-x<sup>2</sup>)?"
This answer, which is -4x, is the first term of the result. Hence, 1st step is:<pre>  4x<sup>3</sup> +  x<sup>2</sup> + 17x - 15 : -x<sup>2</sup> - x - 5 = -4x ...</pre>Next thing to do is to multiply divisor by this term just obtained (-4x) and write the result immediately below the dividend aligning the like terms below each other.<pre>  4x<sup>3</sup> +  x<sup>2</sup> + 17x - 15 : -x<sup>2</sup> - x - 5 = -4x ...
  4x<sup>3</sup> + 4x<sup>2</sup> + 20x</pre>Now, subtract the obtained product from the dividend and write the result immediately below... like this:<pre>  4x<sup>3</sup> +  x<sup>2</sup> + 17x - 15 : -x<sup>2</sup> - x - 5 = -4x ...
-(4x<sup>3</sup> + 4x<sup>2</sup> + 20x)
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      - 3x<sup>2</sup> -  3x - 15</pre>The last line basically shows what is left after the product between the divisor and the temporary result (-4x) is taken away from the dividend.
The rest of the process repeats itself, with the new line being your new dividend.
So, the question is then "What is (-3x<sup>2</sup>)/(-x<sup>2</sup>) and the answer should be 3. So, the next term to add to our temporary result is simply 3.<pre>4x<sup>3</sup> +  x<sup>2</sup> + 17x - 15 : -x<sup>2</sup> - x - 5 = -4x + 3 ...</pre>So, using the same principles, we now multiply this new result (3) by the divisor and write the result immediately below the new dividend.<pre>  4x<sup>3</sup> +  x<sup>2</sup> + 17x - 15 : -x<sup>2</sup> - x - 5 = -4x + 3 ...
-(4x<sup>3</sup> + 4x<sup>2</sup> + 20x)
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      - 3x<sup>2</sup> -  3x - 15
      - 3x<sup>2</sup> -  3x - 15</pre>Subtract the result obtained from the new dividend and write the result immediately below. This will get us:<pre>  4x<sup>3</sup> +  x<sup>2</sup> + 17x - 15 : -x<sup>2</sup> - x - 5 = -4x + 3 ...
-(4x<sup>3</sup> + 4x<sup>2</sup> + 20x)
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      - 3x<sup>2</sup> -  3x - 15
    -(- 3x<sup>2</sup> -  3x - 15)
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                     0</pre>This means that when the product between (-4x + 3) and the divisor is taken away from the original dividend, we are left with 0. So, this clearly means that:<pre>4x<sup>3</sup> +  x<sup>2</sup> + 17x - 15 = (-x<sup>2</sup> - x - 5)(-4x + 3).</pre>We have the result (-4x + 3) and the complete process of obtaining this result is shown once again:<pre>  4x<sup>3</sup> +  x<sup>2</sup> + 17x - 15 : -x<sup>2</sup> - x - 5 = -4x + 3
-(4x<sup>3</sup> + 4x<sup>2</sup> + 20x)
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      - 3x<sup>2</sup> -  3x - 15
    -(- 3x<sup>2</sup> -  3x - 15)
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                     0</pre>