+579 This could technically be classified as off topic but it does have to do with math.
In any math book I work in, I figure out the answer and put it down, but the book always has a different answer, even if the two equations have the same graph! I am in algebra II and this book is driving me INSAAAAANE!
an example of this is shown here:
"Write the expression in factored form: 16-2x^2
I found (4+sqrt(2)x)(4-sqrt(2)x)
The book, however, decided the correct answer was -2(x^2-8)
Don't believe those give the same graph? Go here! https://www.desmos.com/calculator
Enter those three equations and you will see the results.
How do I turn the answer I find into the answer the book wants, and why does the book want a different answer to what I find?
For extra help solving, the book, chapter, page and problem number are listed below.
Book: Algebra 2 Common Core (with a robotic lizard on the cover)
Page: 224
Number: 10
Chapter: 4
If someone could help me figure this out, I would be very grateful.
Also, you can most likely expect more questions out of me in the future. I like knowing how to do everything! 
+633 The book is correct. 16-2x2/2 does equal x2 - 8. What you found equates to the exact same thing. My solution: Both of you are right.
+579 What I want to know is how to decide if the answer I found is the answer the book wants. My teacher counts it wrong even if my solution is correct.
+579 I guess nobody knows, huh? *sigh* Looks like I'll just have to hope my answers are what the book wants.
+128473 OBT - The general rule is to first take out any GCF
So we have
16 - 2x^2
2 [ 8 - x^2 ] which factors as
2 [ √8 - x ] [ √8 + x ] note √8 = 2√2
2 [ 2√2 - x ] [ 2√2 + x ]
Note that WolftamAlpha tends to support the same result as one of its answers :
https://www.wolframalpha.com/input/?i=16+-+2x%5E2
BTW.........the "correct" factorization is sometimes ambiguous.....!!!!!
Your answer is just as "correct" as the book's......
https://www.wolframalpha.com/input/?i=(4%2B+sqrt+(2)x+)+(4+-+sqrt+(2)x)
+579 I understand how to solve it, I don't understand how to find any result the book finds. Wolfram never really finds the answer my book wants cause it goes WAAAY too deep into solving.
+128473 We have factored it as two binomials....
However....I believe the book is focusing on the factors being polynomials with integer coefficients
So
16 - 2x^2 is factored as
2 ( 8 - x^2 )
They also appear to want the polynomial inside the parentheses to be written in order of descending powers....so....this gives
-2 ( x^2 - 8)
Does that help ???
