Homework help!

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Well, since we know the remainder is 5, We can see that x³+30x-c-5 when divided by x-5 leaves no remainder at all.

Given this, we can use knowledge to see that:

(x-5)(x²+5x+55) is equal to x³+30x-c-5.

We can multiply 55 and -5 to get -275, so c is 270.

-Random Person :)   

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BTW THIS WAS AN EDIT, THE ANSWER FOR C is 270 NOT -270!!!

Using sythetic division

5   [     1        0             30            - c   ]

                     5             25          275

       __________________________

           1        5            55             5

Which implies that

275 -  c  = 5

c  = 270