Question

Let u=(5,-12) and c=-3 what is || cu || ?A.-39 B.21 C.39 D.51 i need help badly

Answer 1

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$\mathsf{c}\cdot \overrightarrow{\mathsf{u}}=\mathsf{-\,3\cdot (5,\,-12)}$


Therefore,

$\left\|\mathsf{c}\cdot \overrightarrow{\mathsf{u}}\right\|=\mathsf{\left\|-\,3\cdot (5,\,-12)\right\|}\\\\ \left\|\mathsf{c}\cdot \overrightarrow{\mathsf{u}}\right\|=\mathsf{\left|-\,3\right|\cdot \left\|(5,\,-12)\right\|}\\\\ \left\|\mathsf{c}\cdot \overrightarrow{\mathsf{u}}\right\|=\mathsf{3\cdot \sqrt{5^2+(-12)^2}}$

$\left\|\mathsf{c}\cdot \overrightarrow{\mathsf{u}}\right\|=\mathsf{3\cdot \sqrt{25+144}}\\\\ \left\|\mathsf{c}\cdot \overrightarrow{\mathsf{u}}\right\|=\mathsf{3\cdot \sqrt{169}}\\\\ \left\|\mathsf{c}\cdot \overrightarrow{\mathsf{u}}\right\|=\mathsf{3\cdot \sqrt{13^2}}\\\\ \left\|\mathsf{c}\cdot \overrightarrow{\mathsf{u}}\right\|=\mathsf{3\cdot 13}$

$\left\|\mathsf{c}\cdot \overrightarrow{\mathsf{u}}\right\|=\mathsf{39}\quad\longleftarrow\quad\textsf{this is the answer (option C. 39)}$


I hope this helps. =)

Answer 2

The value of $||c.\overrightarrow {u}||$ is  39 and this can be determined by using the property of dot product and formula to find the vector magnitude.

Given :

• u = (5,-12)
• c = -3

To determine the value of $||c.\overrightarrow {u}||$, calculations is as follows:

$||c.\overrightarrow {u}||$ = $||-3.(5,-12)||$

$||c.\overrightarrow{u}|| = |-3|.||(5,-12)||$

$||c.\overrightarrow{u}|| = |-3|.\sqrt{(5)^2+(-12)^2}$

$||c.\overrightarrow{u}|| = 3.\sqrt{25+144}$

$||c.\overrightarrow{u}|| = 3.\sqrt{169} = 3\times 13$

$||c.\overrightarrow{u}|| = 39$

Therefore, the correct option is C).

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https://brainly.com/question/9523059