Not sure about remainder theorem but I'm sure that the last terms should all multiply tho the last term
see the expanded form is -45
so the last terms of each binomial should multiply to -45
3 times -5 times ?=-45
-15 times ?=-45
divide by -15
?=3
the question mark is 3
Both equations are equivalent, so there are infinitely many solutions.
-
=x
You must find a common denominator(bottom)
×
=
-
=
Your answer is x=