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If [tex]$v = 4i + 5j$[/tex] and [tex]$w = -2i + 3j$[/tex], find [tex]$\operatorname{proj}_{w} v$[/tex]. Then decompose [tex][tex]$v$[/tex][/tex] into its components.

[tex]\operatorname{proj}_{w} v =[/tex] [tex]$\square$[/tex]

(Simplify your answer. Use integers or fractions for any numbers in the expression.)

[tex]v_1 =[/tex] [tex]$\square$[/tex]


Sagot :

Given vectors [tex]\( \mathbf{v} = 4\mathbf{i} + 5\mathbf{j} \)[/tex] and [tex]\( \mathbf{w} = -2\mathbf{i} + 3\mathbf{j} \)[/tex], we need to find the projection of [tex]\( \mathbf{v} \)[/tex] onto [tex]\( \mathbf{w} \)[/tex] and then decompose [tex]\( \mathbf{v} \)[/tex] into its component along [tex]\( \mathbf{w} \)[/tex].

Let's start with the projection calculation:

1. Dot Product:
[tex]\[ \mathbf{v} \cdot \mathbf{w} = (4)(-2) + (5)(3) = -8 + 15 = 7 \][/tex]

2. Magnitude Squared of [tex]\( \mathbf{w} \)[/tex] (also the dot product of [tex]\( \mathbf{w} \)[/tex] with itself):
[tex]\[ \mathbf{w} \cdot \mathbf{w} = (-2)^2 + (3)^2 = 4 + 9 = 13 \][/tex]

3. Projection Formula:
[tex]\[ \operatorname{proj}_{\mathbf{w}} \mathbf{v} = \left( \frac{\mathbf{v} \cdot \mathbf{w}}{\mathbf{w} \cdot \mathbf{w}} \right) \mathbf{w} = \left( \frac{7}{13} \right) \mathbf{w} = \left( \frac{7}{13} \right) (-2\mathbf{i} + 3\mathbf{j}) \][/tex]
So,
[tex]\[ \operatorname{proj}_{\mathbf{w}} \mathbf{v} = \left( \frac{7}{13} \right)(-2\mathbf{i} + 3\mathbf{j}) = \left( -\frac{14}{13} \right)\mathbf{i} + \left( \frac{21}{13} \right) \mathbf{j} \][/tex]

Thus,
[tex]\[ \operatorname{proj}_{\mathbf{w}} \mathbf{v} = \left( -\frac{14}{13}\mathbf{i} + \frac{21}{13}\mathbf{j} \right) \][/tex]
Simplifying, we round to approximate decimal values:
[tex]\[ \operatorname{proj}_{\mathbf{w}} \mathbf{v} \approx -1.07692308\mathbf{i} + 1.61538462\mathbf{j} \][/tex]
Let's assign this to [tex]\( v_1\)[/tex]:
[tex]\[ v_1 = \operatorname{proj}_{\mathbf{w}} \mathbf{v} = \left( -\frac{14}{13}\mathbf{i} + \frac{21}{13}\mathbf{j} \right) \][/tex]

So, in summary:
[tex]\[ \operatorname{proj}_{\mathbf{w}} \mathbf{v} = -\frac{14}{13} \mathbf{i} + \frac{21}{13} \mathbf{j} \][/tex]

And,
[tex]\[ v_1 = -\frac{14}{13} \mathbf{i} + \frac{21}{13} \mathbf{j} \][/tex]

Or approximately:
[tex]\[ v_1 \approx -1.07692308 \mathbf{i} + 1.61538462 \mathbf{j} \][/tex]
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