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SAT
Course: SAT > Unit 10
Lesson 2: Passport to advanced mathematics- Solving quadratic equations — Basic example
- Solving quadratic equations — Harder example
- Interpreting nonlinear expressions — Basic example
- Interpreting nonlinear expressions — Harder example
- Quadratic and exponential word problems — Basic example
- Quadratic and exponential word problems — Harder example
- Manipulating quadratic and exponential expressions — Basic example
- Manipulating quadratic and exponential expressions — Harder example
- Radicals and rational exponents — Basic example
- Radicals and rational exponents — Harder example
- Radical and rational equations — Basic example
- Radical and rational equations — Harder example
- Operations with rational expressions — Basic example
- Operations with rational expressions — Harder example
- Operations with polynomials — Basic example
- Operations with polynomials — Harder example
- Polynomial factors and graphs — Basic example
- Polynomial factors and graphs — Harder example
- Nonlinear equation graphs — Basic example
- Nonlinear equation graphs — Harder example
- Linear and quadratic systems — Basic example
- Linear and quadratic systems — Harder example
- Structure in expressions — Basic example
- Structure in expressions — Harder example
- Isolating quantities — Basic example
- Isolating quantities — Harder example
- Function notation — Basic example
- Function notation — Harder example
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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?(6 votes)
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)?(4 votes)
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).(2 votes)
- 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(2 votes)
- why couldnt it be answer C because that answer choice is the same thing, just simplified(2 votes)
- 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(2 votes)
- 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
?(0 votes) 
why does he speak so fast its hard to consume the info?(0 votes)- Plz explain it for me …...thanks a lot(0 votes)
Video transcript
- [Instructor] We're asked
in the equation above, b and c are constants. What is the value of b + c? And they give us the equation over here. So, pause this video and see
if you can have a go at that before we work through this together. All right, now let's work
through this together. And it looks like what's
happening is we have a quadratic on the left and then on the right we
have that same quadratic that is factored out, although they don't
tell us what b and c are we have to figure that out. So, one way to tackle this is
actually let me just rewrite the left-hand side of this. So, it is 2x squared + 16x + 30. And what I wanna do is try to get as close to the form that I have
on the right as possible. So, it looks like they factored out a two. So, let me do that. So, this is equal to two times. And if any of this factoring of quadratics is unfamiliar to you, I encourage you to review
that on Khan Academy, on The non-ACT portion of Khan
Academy to get the basics. But if we factor out of
two out of this first term, you're just left with an X squared. You factor out of two
out of 16x, you get 8x. And you factor a two out
of 30 and you get + 15. And then it looks like what they have done is they have factored this part into x + b X x + c. And the simplest way to factor
things is to say, all right, are there two numbers that
when I add them, I get eight, and that when I multiply them, I get 15? And those two numbers are
actually going to be b and c this is one of our main
factoring techniques. So, b + c needs to be equal to eight, and b X c needs to be equal to 15. And if we figure that out,
then we can factor completely. Well, we've just actually
answered their question, b + c needs to be equal to eight. And so, eight is the answer. Now, let me just factor
this out completely, so that you can see that a
little bit more completely. I'm using the word completely a lot. So, if I were to factor this out, this is the same thing as two times the two numbers
that add up to eight. And when I multiply them, I get 15, let's see three and five seemed to work. So, it's gonna be two times X plus three times X plus five. You can verify that three times five you're gonna get that 15 there. And then when you multiply
these two binomials, you're gonna get 3x + 5x, which is going to be 8x. And so, you can see that you
can either treat b as three and c is five or b is five and c is three, but either way, b + c is
going to be equal to eight.