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Solution: Let $ \vec{OA} = \mathbf{a} $, $ \vec{OB} = \mathbf{b} $. Then $ \overrightarrow{OC} = m\mathbf{a} + n\mathbf{b} $. For $ \overrightarrow{OC} \perp (\mathbf{a} - \mathbf{b}) $, their dot product is zero: $ (m\mathbf{a} + n\mathbf{b}) \cdot (\mathbf{a} - \mathbf{b}) = 0 $. Expand: $ m\|\mathbf{a}\|^2 - m\mathbf{a} \cdot \mathbf{b} + n\mathbf{b} \cdot \mathbf{a} - n\|\mathbf{b}\|^2 = 0 $. Substitute $ \|\mathbf{a}\| = 2 $, $ \|\mathbf{b}\| = 3 $, $ \mathbf{a} \cdot \mathbf{b} = 2 \cdot 3
\boxed{(6, 1)}Question: A hydrologist studying groundwater flow measures the volume of water (in liters) passing through a sensor at different times, recording values that are positive multiples of 5. If the cube of one such measurement is less than 1500, what is the greatest possible value of that measurement?
Solution: Let the measurement be $ u $, a positive multiple of 5 such that $ u^3 < 1500 $.
We test successive multiples of 5:
$ u = 5 $: $ 5^3 = 125 $
$ u = 10 $: $ 10^3 = 1000 $
$ u = 15 $: $ 15^3 = 3375 $, which exceeds 1500.
Thus, the greatest multiple of 5 satisfying $ u^3 < 1500 $ is $ u = 10 $.
Therefore, the greatest possible value is $ \boxed{10} $.
Question: A palynologist analyzing pollen counts observes that the average of three counts — $ 3u+2 $, $ 5u+7 $, and $ 4u+1 $ — equals 62. What is the value of $ u $?