Find the greatest common divisor

d(x) of

f(x) = x^5 − 2x^4 − 3x^3 − 15x^2 + 10x + 25

and

g(x) = x^4 − 6x^2 − 24^x − 35

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using the polynomial long division

f(x) / g (x)

i ended up with 3x^3 + 135 x^2 -513x -815

couldn't factorise further !

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the step after that

x^4 − 6x^2 − 24^x − 35 / 3x^3 + 135 x^2 -513x -815

and the answer was -13275x^2 -53578x+9150

but I don't know what should I do after that to get the gcd ,

and I'm not sure if my work is alright ..

any help ?

thnx