Given vector $\vec{a}=(1, \sqrt{3})$ and the angle between $\vec{a}$ and $\vec{b}$ is $\frac{\pi}{6}$, find the projection of $\vec{a}$ on $\vec{b}$.

GeometryVectorsProjectionsDot ProductTrigonometry
2025/3/27

1. Problem Description

Given vector a=(1,3)\vec{a}=(1, \sqrt{3}) and the angle between a\vec{a} and b\vec{b} is π6\frac{\pi}{6}, find the projection of a\vec{a} on b\vec{b}.

2. Solution Steps

Let the projection of a\vec{a} on b\vec{b} be projbaproj_{\vec{b}} \vec{a}.
The formula for the projection of a\vec{a} on b\vec{b} is:
projba=acosθproj_{\vec{b}} \vec{a} = |\vec{a}| \cos{\theta}, where θ\theta is the angle between a\vec{a} and b\vec{b}.
We are given that a=(1,3)\vec{a} = (1, \sqrt{3}). Therefore, the magnitude of a\vec{a} is:
a=12+(3)2=1+3=4=2|\vec{a}| = \sqrt{1^2 + (\sqrt{3})^2} = \sqrt{1 + 3} = \sqrt{4} = 2.
The angle between a\vec{a} and b\vec{b} is given as θ=π6\theta = \frac{\pi}{6}.
Therefore, cosπ6=32\cos{\frac{\pi}{6}} = \frac{\sqrt{3}}{2}.
Now, we can compute the projection of a\vec{a} on b\vec{b}:
projba=acosθ=232=3proj_{\vec{b}} \vec{a} = |\vec{a}| \cos{\theta} = 2 \cdot \frac{\sqrt{3}}{2} = \sqrt{3}.

3. Final Answer

The projection of a\vec{a} on b\vec{b} is 3\sqrt{3}.

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