Discover how IDNLearn.com can help you find the answers you need quickly and easily. Join our community to receive prompt and reliable responses to your questions from experienced professionals.

20. The position vectors of points [tex]$A$[/tex] and [tex]$B$[/tex] with respect to the origin [tex]$O$[/tex] are [tex]$\binom{-8}{5}$[/tex] and [tex]$\binom{12}{-5}$[/tex] respectively. Point [tex]$M$[/tex] is the midpoint of [tex]$AB$[/tex] and [tex]$N$[/tex] is the midpoint of [tex]$OA$[/tex].

a) Find:
(i) the coordinates of [tex]$N$[/tex] and [tex]$M$[/tex] (3 marks)
(ii) the magnitude of [tex]$NM$[/tex] (3 marks)

b) Express vector [tex]$NM$[/tex] in terms of [tex]$OB$[/tex] (1 mark)

c) Point [tex]$P$[/tex] maps onto [tex]$P^{\prime}$[/tex] by a translation [tex]$\binom{-5}{8}$[/tex]. Given that [tex]$OP = OM + 2MN$[/tex], find the coordinates of [tex]$P^{\prime}$[/tex].


Sagot :

### a) (i) Find the coordinates of [tex]\(N\)[/tex] and [tex]\(M\)[/tex]

Coordinates of [tex]\(N\)[/tex]:

The point [tex]\(N\)[/tex] is the midpoint of the line segment [tex]\(OA\)[/tex].

Given:
[tex]\[ O = \binom{0}{0} \][/tex]
[tex]\[ A = \binom{-8}{5} \][/tex]

The midpoint [tex]\(N\)[/tex] is calculated as:
[tex]\[ N = \frac{O + A}{2} = \frac{\binom{0}{0} + \binom{-8}{5}}{2} = \binom{\frac{0 + (-8)}{2}}{\frac{0 + 5}{2}} = \binom{-4}{2.5} \][/tex]

So, the coordinates of [tex]\(N\)[/tex] are [tex]\(\binom{-4}{2.5}\)[/tex].

Coordinates of [tex]\(M\)[/tex]:

The point [tex]\(M\)[/tex] is the midpoint of the line segment [tex]\(AB\)[/tex].

Given:
[tex]\[ A = \binom{-8}{5} \][/tex]
[tex]\[ B = \binom{12}{-5} \][/tex]

The midpoint [tex]\(M\)[/tex] is calculated as:
[tex]\[ M = \frac{A + B}{2} = \frac{\binom{-8}{5} + \binom{12}{-5}}{2} = \binom{\frac{-8 + 12}{2}}{\frac{5 + (-5)}{2}} = \binom{2}{0} \][/tex]

So, the coordinates of [tex]\(M\)[/tex] are [tex]\(\binom{2}{0}\)[/tex].

---
### a) (ii) Find the magnitude of [tex]\(NM\)[/tex]

Vector [tex]\(NM\)[/tex]:

First, we find vector [tex]\(NM\)[/tex]:
[tex]\[ N = \binom{-4}{2.5} \][/tex]
[tex]\[ M = \binom{2}{0} \][/tex]

[tex]\[ NM = M - N = \binom{2 - (-4)}{0 - 2.5} = \binom{6}{-2.5} \][/tex]

Magnitude of [tex]\(NM\)[/tex]:

The magnitude of a vector [tex]\(\binom{a}{b}\)[/tex] is given by [tex]\( \sqrt{a^2 + b^2} \)[/tex]:
[tex]\[ ||NM|| = \sqrt{6^2 + (-2.5)^2} = \sqrt{36 + 6.25} = \sqrt{42.25} = 6.5 \][/tex]

So, the magnitude of [tex]\(NM\)[/tex] is [tex]\(6.5\)[/tex].

---
### b) Express vector [tex]\(NM\)[/tex] in terms of [tex]\(OB\)[/tex]

Vector [tex]\(OB\)[/tex]:

Given:
[tex]\[ O = \binom{0}{0} \][/tex]
[tex]\[ B = \binom{12}{-5} \][/tex]

[tex]\[ OB = B - O = \binom{12}{-5} - \binom{0}{0} = \binom{12}{-5} \][/tex]

We know [tex]\( NM = \binom{6}{-2.5} \)[/tex].

The vector [tex]\(NM\)[/tex] in terms of [tex]\(OB\)[/tex] is:
[tex]\[ NM = \frac{\binom{6}{-2.5}}{|OB|} \cdot OB \][/tex]
where [tex]\( |OB| \)[/tex] is the magnitude of [tex]\(OB\)[/tex]:
[tex]\[ |OB| = \sqrt{12^2 + (-5)^2} = \sqrt{144 + 25} = \sqrt{169} = 13 \][/tex]

[tex]\[ NM = \frac{\binom{6}{-2.5}}{13} \][/tex]

So, [tex]\( NM = \frac{6}{13} \binom{12}{-5} \)[/tex].

Thus, vector [tex]\(NM\)[/tex] in terms of [tex]\(OB\)[/tex] is [tex]\(\frac{6}{13} OB\)[/tex].

---
### c) Given [tex]\(OP = OM + 2MN\)[/tex], find the coordinates of [tex]\(P'\)[/tex].

Given:
[tex]\[ OP = OM + 2 MN \][/tex]

First, we find [tex]\(OM\)[/tex]:
[tex]\[ OM = M - O = \binom{2}{0} - \binom{0}{0} = \binom{2}{0} \][/tex]

Next, we find [tex]\(MN\)[/tex]:
[tex]\[ MN = N - M = \binom{-4}{2.5} - \binom{2}{0} = \binom{-4 - 2}{2.5 - 0} = \binom{-6}{2.5} \][/tex]

Given:
[tex]\[ OP = OM + 2 MN \][/tex]

Substitute the values:
[tex]\[ OP = \binom{2}{0} + 2 \binom{-6}{2.5} = \binom{2}{0} + \binom{-12}{5} = \binom{2 - 12}{0 + 5} = \binom{-10}{5} \][/tex]

Lastly, apply the translation to find [tex]\(P'\)[/tex]:
[tex]\[ \text{Translation} = \binom{-5}{8} \][/tex]
[tex]\[ P' = OP + \text{Translation} = \binom{-10}{5} + \binom{-5}{8} = \binom{-10 - 5}{5 + 8} = \binom{-15}{13} \][/tex]

So, the coordinates of [tex]\(P'\)[/tex] are [tex]\(\binom{9}{3}\)[/tex].