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MathNet 2018-part-05 — 181 problems (EN–VI) Question 135

Math Olympiad Vault · MathNet 2018-part-05 — 181 problems (EN–VI)

Question 135

We are given two vectors of equal length $\frac{1}{3} \vec{a}+\vec{b}$ and $\frac{2}{3} \vec{a}+\vec{b}$, where $\vec{a}$ and $\vec{b}$ are nonzero vectors such that $|\vec{a}|=\sqrt{3}|\vec{b}|$.

a) Compute the size of the angle between the vectors $\vec{a}$ and $\vec{b}$.

b) Compute the size of the angle between the vectors $\frac{1}{3} \vec{a}+\vec{b}$ and $\frac{2}{3} \vec{a}+\vec{b}$.