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u=(2,5)\vec{u} = (-2,5)\newlineFind the direction angle of u\vec{u}. \newlineEnter your answer as an angle in degrees between 00^\circ and 360360^\circ rounded to the nearest hundredth.\newlineθ=\theta = \square^\circ

Full solution

Q. u=(2,5)\vec{u} = (-2,5)\newlineFind the direction angle of u\vec{u}. \newlineEnter your answer as an angle in degrees between 00^\circ and 360360^\circ rounded to the nearest hundredth.\newlineθ=\theta = \square^\circ
  1. Identify Formula: Identify the formula for the direction angle of a vector. The direction angle θ\theta of a vector u=(x,y)\vec{u}=(x,y) can be found using the arctangent function: θ=arctan(yx)\theta = \text{arctan}(\frac{y}{x}). However, since arctan\text{arctan} only gives values from 90-90^{\circ} to 9090^{\circ}, we need to adjust the angle based on the quadrant in which the vector lies.
  2. Calculate Arctangent: Calculate the arctangent of the y-coordinate divided by the x-coordinate.\newlineFor u=(2,5)\vec{u}=(-2,5), we have x=2x=-2 and y=5y=5. Thus, θ=arctan(52)=arctan(2.5)\theta = \arctan\left(\frac{5}{-2}\right) = \arctan(-2.5).\newlineUsing a calculator, we find that arctan(2.5)68.20\arctan(-2.5) \approx -68.20^\circ.
  3. Adjust Based on Quadrant: Adjust the angle based on the quadrant.\newlineSince the x-coordinate is negative and the y-coordinate is positive, u\vec{u} lies in the second quadrant. In the second quadrant, we must add 180180^{\circ} to the arctangent value to find the correct direction angle.\newlineTherefore, θ=68.20+180=111.80\theta = -68.20^{\circ} + 180^{\circ} = 111.80^{\circ}.
  4. Ensure Angle Range: Ensure the angle is within the range 00^{\circ} to 360360^{\circ}. The calculated angle, 111.80111.80^{\circ}, is already within the desired range. Therefore, no further adjustments are needed.

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