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Manipulating quadratic and exponential expressions — Harder example

Watch Sal work through a harder Manipulating quadratic and exponential expressions problem.

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• Can someone help me with this beginning to end?. i dont understand ho to do any of this.
• It's confusing when he says "nonpositive" or "nonnegative" why wouldn't just say negative and positive?
• From where in khan academy i can get explanation about w= -b/2a which sal used at 6.40
• Check it out on Quadratic Functions. It is derived from the Completing Square Method.
Anyway, the sum of roots of a quadratic equation = -b/a
Vertex lies on axis of symmetry, midway between the two roots,
So, abscissa of vertex = -b/2a

As far as I remember, it was covered on the Parabola section in Quadratic functions tutorial.
• what should do i am getting 1400 in collegeboard exams but I am getting only 1200 in kaplan and barron tests.
• I recommend to do as much as prep books/questions as you can. Especially understand the 'syllabus' and what's required of you to learn. Finish all of Khan Academy's exercises, correct your errors, learn time conservation methods and practice!! Keep on practicing!
• Why did it have to be 50?
• How'd he get 100w at 0.51?? 50 squared is 2500.
(1 vote)
• What he did was he expanded (w-50)^2. This is how you do it:
(w-50)(w-50)
w^2-50w-50w+2500
w^2-100w+2500
He didn't show the steps and combined the -50w and -50w. He then did 50^2 which is 2500.
Hope this helps!
• Another way to get this is that, this is the "completing square" form, therefore its easier to get the maximum point. Like he said, vertex form.
• in he's getting 100 out of nowhere. Can anyone pls explain!
• There, Sal is applying a property of squared binomials:
(a + b)^2 = a^2 + 2*a*b + b^2
This essentially takes a step out of foiling the two binomials together. -100w is the middle term, (2)(-50)(w).