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If a = pi +3j - 7k, b = pi - pj +4k and the angle between a and is acute then the possible values for p are given by​

Sagot :

xero099

Answer:

The family of possible values for [tex]p[/tex] are:

[tex](-\infty, -4) \,\cup \,(7, +\infty)[/tex]

Step-by-step explanation:

By Linear Algebra, we can calculate the angle by definition of dot product:

[tex]\cos \theta = \frac{\vec a\,\bullet\,\vec b}{\|\vec a\|\cdot \|\vec b\|}[/tex] (1)

Where:

[tex]\theta[/tex] - Angle between vectors, in sexagesimal degrees.

[tex]\|\vec a\|, \|\vec b \|[/tex] - Norms of vectors [tex]\vec {a}[/tex] and [tex]\vec{b}[/tex]

If [tex]\theta[/tex] is acute, then the cosine function is bounded between 0 a 1 and if we know that [tex]\vec {a} = (p, 3, -7)[/tex] and [tex]\vec {b} = (p, -p, 4)[/tex], then the possible values for [tex]p[/tex] are:

Minimum ([tex]\cos \theta = 0[/tex])

[tex]\frac{p^{2}-3\cdot p -28}{\sqrt{p^{2}+58}\cdot \sqrt{2\cdot p^{2}+16}} > 0[/tex]

Maximum ([tex]\cos \theta = 1[/tex])

[tex]\frac{p^{2}-3\cdot p -28}{\sqrt{p^{2}+58}\cdot \sqrt{2\cdot p^{2}+16}} < 1[/tex]

With the help of a graphing tool we get the family of possible values for [tex]p[/tex] are:

[tex](-\infty, -4) \,\cup \,(7, +\infty)[/tex]

View image xero099

The dot product between the two vectors is the product of the magnitude between them times cosine angle.

The possible values for [tex]p[/tex] is (7,-4), when the angle is acute between [tex]a[/tex] and [tex]b[/tex].

To find the value of [tex]p[/tex] we need to perform the dot product of two equation.

How do you multiply vector in dot product?

The dot product between the two vectors is the product of the magnitude between them times cosine angle

Given information-

The vector equation given in the problem is,

[tex]a = p\hat i +3\hat j - 7\hat k[/tex]

[tex]b = p\hat i - p\hat j +4\hat k[/tex]

For acute angle, the dot product of [tex]a,b[/tex] less than equal to zero.

Thus,

[tex]a .b<0[/tex]

Put the values,

[tex](p\hat i +3\hat j - 7\hat k)(p\hat i - p\hat j +4\hat k)<0[/tex]

In the dot product the multiplication of different unit vector is zero. Thus,

[tex]p^2-3p-28<0[/tex]

Factorize above equation using the split the middle term method as,

[tex]p^2-7p+4p-28<0\\(p-7)(p+4)<0[/tex]

As the factor of the above equation is 7 and -4.

Thus the possible values for [tex]p[/tex] is (7,-4), when the angle is acute between [tex]a[/tex] and [tex]b[/tex].

Learn more about the dot product here;

https://brainly.com/question/9956772

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