
Notice that if

, then

. Recall the definition of the derivative of a function

at a point

:

So the value of this limit is exactly the value of the derivative of

at

.
You have
Answer 28.
Possible values for the three factors of -3
- 1, -1 and 3
- -1.5, 1 and 2
- 1.5, -1 and 2
- 1.5, 1 and -2
Answer 29.
The product of two nonzero integers will be less than or equal to both of the integers if they are multiplied by number itself and one or by number itself and one with negative sign.
Answer 30.
The sign of the product of three integers with the same sign will be positive or negative. If odd number of same sign is multiplied, the product will be of that sign.
(+) (+) (+) = (+)
(-) (-) (-) = (-)
There's no if about it,

has a zero

so

is a factor. That's the special case of the Remainder Theorem; since

we'll get a remainder of zero when we divide

by

At this point we can just divide or we can try more little numbers in the function. It doesn't take too long to discover

too, so

is a factor too by the remainder theorem. I can find the third zero as well; but let's say that's out of range for most folks.
So far we have

where

is the zero we haven't guessed yet. Again we could divide

by

but just looking at the constant term we must have

so

We check

We usually talk about the zeros of a function and the roots of an equation; here we have a function

whose zeros are
57+23 = 80
not rounded it's 80.14