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On third one, what is going on is we have 4 terms from using FOIL on two binomials. But we notice that there is no square term. So what happened is that one of the binomials is (x ) and other is (y ). So the F of FOIL gives us the xy. Then we have to figure out the rest. We notice the number is -10, so the two numbers we must fill in are either -2 and 5 or -5 and 2. (There are 4 ways that could be tried)
So we set it up:
(x - 2)(y + 5) = xy -2y + 5x -10.
Not correct, we also notice that the y has -5 and x has the 2. So how can the binomials be set up to give that? Answer is we put the -5 with the x and the 2 with the y:
(x - 5)(y + 2) = xy - 5y + 2x - 10
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Last one is a difference of two squares, x^4 and 16. There is a formula for this:
(x^2 + 4)(x^2 - 4).
The second binomial is also difference of squares. It breaks down into (x + 2)(x - 2)
So the final is (x^2 + 4)(x + 2)(x - 2).
Also www.purplemath.com is a good site. Your library may also have a link to homework help, which in many libraries links you with tutor.com. That sets up a live turoring session where someone can help you that way.