How do you use the remainder theorem and synthetic division to find the remainder when x^3 - 2x^2 + 5x - 6 div x - 3?

1 Answer
Sep 22, 2015

Here is the synthetic division.

Explanation:

(Division format from Ernest Z. here on Socratic)

Step 1. Write only the coefficients of x in the dividend inside an upside-down division symbol.

color(white)(1)|1" "-2color(white)(XX)5" "" "-6
color(white)(1)|" "color(white)(X)
" "stackrel("—————————————)

Step 2. Put the constant in the divisor x-c at the left. In this case c=3

3|1" "-2color(white)(XX)5" "" "-6
color(white)(1)|" "color(white)(X)
" "stackrel("—————————————)

Step 3. Drop the first coefficient of the dividend below the division symbol.

3|1" "-2color(white)(XX)5" "" "-6
color(white)(1)|" "color(white)(X)
" "stackrel("—————————————)
color(white)(1)|1

Step 4. Multiply the result by the constant, and put the product in the next column.

3|1" "-2color(white)(XX)5" "" "-6
color(white)(1)|" "color(white)(X1)3
" "stackrel("—————————————)
color(white)(1)|1

Step 5. Add down the column.

3|1" "-2color(white)(XX)5" "" "-6
color(white)(1)|" "color(white)(X1)3" "
" "stackrel("—————————————)
color(white)(1)|1" "" "1

Step 6. Repeat Steps 4 and 5 until you can go no farther.

3|1" "-2color(white)(XX)5" "color(white)(1)-6
color(white)(1)|" "color(white)(X1)3" "color(white)(X1)3color(white)(XX1)24
" "stackrel("—————————————)
color(white)(1)|1" "color(white)(X)1" "color(white)(X1)8" ""|"color(white)(X1)18

The remainder is 18

(And the quotient is 1x^2+1x+8, more commonly written x^2+x+8)