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​

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]

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.

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;

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