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# Structure in expressions — Basic example

Watch Sal work through a basic Structure in expressions problem.

## Want to join the conversation?

• Isn't the answer -8, but not 8 as it mentioned in the video? Because, having formula ax^2+bx+c ( in our example x^2+8x+15), the sum of x1 and x2 must be equal to -b ( in our example b+c=-8) Why then here we have +8 in the example?
• This can work however -b/a would be equal to -b-c because the roots are -b and -c, not b and c.
-b-c = -8
b+c = 8
(1 vote)
• (p+1)^2 can be factored as (p^2+2p+1^2)?
• Yes. expanding this equation makes it look like the below equation:
(p + 1) (p + 1)
(p + 1) (p + 1) = p^2 + p + p + 1^2 = p^2 + 2p + 1

Basically, the parentheses mean you are squaring the whole equation.
If you wanted to square P and 1 separately though, it would look more like this:
P^2 + 1^2 (which is simply P^2 + 1).
• I know how to factor just fine, but its my intuition that fails me. I wouldn't know what the first step to solving this would be
• why couldnt it be answer C because that answer choice is the same thing, just simplified
• I think that The answer is -8
(1 vote)
• I am guessing just like the comment by Alice, you tried to find it by using -b/a
This can work however -b/a would be equal to -b-c because the roots are -b and -c, not b and c.
-b-c = -8
b+c = 8
• Can't we use calc for this problem in the exam
(1 vote)
• I don’t happen to see a way to use Calculus here, but go ahead if you can get consistently correct answers. The SAT will never require any Calculus knowledge, though.
(1 vote)
• Can't you factor out a^2-b^ as (a-b)(a+b)?
(1 vote)
• Yes, a^2 - b^2 can be factored out as (a+b)(a-b)
(1 vote)
• If
a(x+b)2=3x2+36x+ca(x+b)^2 = 3x^2+36x+c
a(x+b)
2
=3x
2
+36x+c
a, left parenthesis, x, plus, b, right parenthesis, start superscript, 2, end superscript, equals, 3, x, start superscript, 2, end superscript, plus, 36, x, plus, c
, what is the value of
cc
c
c
?