Remainder Theorem for f(-1), given f(x) = -x^4 + ...

[Prostagma]

Hello, I'm familiar with the remainder theorem, but I was wondering what I was doing wrong when solving this question:

Given f(x)= -x^4 + 3x^3 + 5x^2 - 10 find f(-1)

I used the Remainder Theorem: I got a remainder of -9, which means that f(-1)= -9, but when I plug -1 into the original function -x^4+3x^3+5x^2-10, it doesn't give me -9. (Sorry the spacing in the division is weird, I don't know how to format it)

-1 | -1  3   5   0  -10
   |     1  -4  -1    1
   --------------------
     -1  4   1  -1   -9

This gives me --> -(-1^4) + (3*-1^3) + (5*-1^2) -10 = 1 - 3 - 5 - 10 = -17

I'm confused, because the Remainder Theorem works on other examples I was taught in class.

 

[wjm11]

Hello, I'm familiar with the remainder theorem, but I was wondering what I was doing wrong when solving this question:

Given f(x)= -x^4+3x^3+5x^2-10 find f(-1)

I used the remainder theorem: I got a remainder of -9, which means that f(-1)= -9, but when I plug -1 into the original function -x^4+3x^3+5x^2-10, it doesn't give me -9

-1| -1 3 5 0 -10
1 -4 -1 1
----------------------
-1 4 1 -1 -9

it gives me --> -(-1^4) + (3*-1^3) + (5*-1^2) -10
1-3-5-10= -17

You got everything right except your final calculation:

-(-1^4) + (3*-1^3) + (5*-1^2) –10
= -1 –3 + 5 –10 = -9

 

[Prostagma]

Thank you

Ah thank you so much, that question was bothering me. I get confused with the negatives and what not =(