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  • - [Instructor] We are asked, what could

  • be the equation of p?

  • And we have graph of our polynomial p right over here,

  • you could view this as the graph

  • of y is equal to p of x.

  • So pause this video and see if you can figure that out.

  • All right, now let's work on this together,

  • and you can see that all the choices have p of x,

  • in factored form where it's very easy

  • to identify the zeros or the x values

  • that would make our polynomial equal to zero.

  • And we could also look at this graph

  • and we can see what the zeros are.

  • This is where we're going to intersect the x-axis,

  • also known as the x-intercepts.

  • So you can see when x is equal to negative four,

  • we have a zero because our polynomial is zero there.

  • So we know p of negative four is equal to zero.

  • We also know that p of, looks like 1 1/2,

  • or I could say 3/2.

  • p of 3/2 is equal to zero,

  • and we also know that p of three is equal to zero.

  • So let's look for an expression where that is true.

  • And because it's in factored form,

  • each of the parts of the product

  • will probably make our polynomial zero

  • for one of these zeroes.

  • So let's see if, if in order for our polynomial

  • to be equal to zero when x is equal to negative four,

  • we probably want to have a term

  • that has an x plus four in it.

  • Or we want to have a, I should say,

  • a product that has an x plus four in it.

  • Because x plus four is equal

  • to zero when x is equal to negative four.

  • Well we have an x plus four there,

  • and we have an x plus four there.

  • So I'm liking choices B and D so far.

  • Now for this second root, we have p of 3/2

  • is equal to zero so I would look

  • for something like x minus 3/2 in our product.

  • I don't see an x minus 3/2 here,

  • but as we've mentioned in other videos

  • you can also multiply these times constants.

  • So if I were to multiply,

  • let's see to get rid of this fraction here,

  • if I multiply by two this would be the same thing as,

  • let me scroll down a little bit,

  • same thing as two x minus three.

  • And you could test that out,

  • two x minus three is equal to zero when x is equal to 3/2.

  • And let's see, we have a two x minus three right over there.

  • So choice D is looking awfully good,

  • but let's just verify it with this last one.

  • For p of three to be equal to zero,

  • we could have an expression

  • like x minus three in the product

  • because this is equal to zero when x is equal to three,

  • and we indeed have that right over there.

  • So choice D is looking very good.

  • When x is equal to negative four,

  • this part of our product is equal

  • to zero which makes the whole thing equal to zero.

  • When x is equal to 3/2, two x minus three is equal

  • to zero which makes the entire product equal to zero.

  • And when x minus, and when an x is equal to three,

  • it makes x minus three equal to zero.

  • Zero times something, times something

  • is going to be equal to zero.

- [Instructor] We are asked, what could

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A2 初級

多項式的零點:方程與圖形的匹配|代數2|可汗學院 (Zeros of polynomials: matching equation to graph | Polynomial graphs | Algebra 2 | Khan Academy)

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    林宜悉 發佈於 2021 年 01 月 14 日
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