20x^4-39x^3-16x
Make sure to multiply all the terms by each other in the two parentheses
To find the difference, we are going to destroy the parenthesis first, and then, we are going to perform the operations. Remember that to destroy a parenthesis preceded by a negative sign (-), you should change the signs of the factors inside the parenthesis:


Now we can factor both numerator and denominator and simplify:

We can conclude that the difference in simplest form is:
We can see both terms have a (x-2) in them.
We can also see that 8 and 2 are both even so there is a 2 in common.
This means that the gcd or hcf or whatever you call it is 2(x-2)
**Just mentioning most of the time we call it the GCD(greatest common divisor) or the GCF(greatest common factor) and almost never uses hcf :)
Angle ACF complementary, because it's angle equals up to 90.and FCB is complementary also, because the angle equals 90. hope i helped.