SOLUTION: What is the quotient when x^4 - 4x^2 + 7x +15 is divided by x+4

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Question 92220: What is the quotient when x^4 - 4x^2 + 7x +15 is divided by x+4
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

Start with the given polynomial %28x%5E4+-+4x%5E2+%2B+7x+%2B+15%29%2F%28x%2B4%29

First lets find our test zero:

x%2B4=0 Set the denominator x%2B4 equal to zero

x=-4 Solve for x.

so our test zero is -4


Now set up the synthetic division table by placing the test zero in the upper left corner and placing the coefficients of the numerator to the right of the test zero.(note: remember if a polynomial goes from 1x%5E4 to -4x%5E2 there is a zero coefficient for x%5E3. This is simply because x%5E4+-+4x%5E2+%2B+7x+%2B+15 really looks like 1x%5E4%2B0x%5E3%2B-4x%5E2%2B7x%5E1%2B15x%5E0
-4|10-4715
|

Start by bringing down the leading coefficient (it is the coefficient with the highest exponent which is 1)
-4|10-4715
|
1

Multiply -4 by 1 and place the product (which is -4) right underneath the second coefficient (which is 0)
-4|10-4715
|-4
1

Add -4 and 0 to get -4. Place the sum right underneath -4.
-4|10-4715
|-4
1-4

Multiply -4 by -4 and place the product (which is 16) right underneath the third coefficient (which is -4)
-4|10-4715
|-416
1-4

Add 16 and -4 to get 12. Place the sum right underneath 16.
-4|10-4715
|-416
1-412

Multiply -4 by 12 and place the product (which is -48) right underneath the fourth coefficient (which is 7)
-4|10-4715
|-416-48
1-412

Add -48 and 7 to get -41. Place the sum right underneath -48.
-4|10-4715
|-416-48
1-412-41

Multiply -4 by -41 and place the product (which is 164) right underneath the fifth coefficient (which is 15)
-4|10-4715
|-416-48164
1-412-41

Add 164 and 15 to get 179. Place the sum right underneath 164.
-4|10-4715
|-416-48164
1-412-41179

Since the last column adds to 179, we have a remainder of 179. This means x%2B4 is not a factor of x%5E4+-+4x%5E2+%2B+7x+%2B+15
Now lets look at the bottom row of coefficients:

The first 4 coefficients (1,-4,12,-41) form the quotient

x%5E3+-+4x%5E2+%2B+12x+-+41

and the last coefficient 179, is the remainder, which is placed over x%2B4 like this

179%2F%28x%2B4%29



Putting this altogether, we get:

x%5E3+-+4x%5E2+%2B+12x+-+41%2B179%2F%28x%2B4%29

So

which looks like this in remainder form:
%28x%5E4+-+4x%5E2+%2B+7x+%2B+15%29%2F%28x%2B4%29=x%5E3+-+4x%5E2+%2B+12x+-+41 remainder 179


You can use this online polynomial division calculator to check your work