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Find the direction angle of u=(10,7) \mathbf{u} = (-10,7) . Enter your answer as an angle in degrees between 0 0^\circ and 360 360^\circ rounded to the nearest hundredth.

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Q. Find the direction angle of u=(10,7) \mathbf{u} = (-10,7) . Enter your answer as an angle in degrees between 0 0^\circ and 360 360^\circ rounded to the nearest hundredth.
  1. Definition of Direction Angle: The direction angle of a vector in the plane is the angle measured counterclockwise from the positive xx-axis to the vector. To find this angle, we use the arctangent function, which gives us the angle whose tangent is the ratio of the yy-coordinate to the xx-coordinate of the vector.
  2. Calculate Tangent Ratio: For the vector u=(10,7)\mathbf{u} = (-10,7), the x-coordinate is 10-10 and the y-coordinate is 77. The tangent of the direction angle θ\theta is therefore tan(θ)=710=0.7\tan(\theta) = \frac{7}{-10} = -0.7.
  3. Use Arctangent Function: We use the arctangent function to find the angle θ\theta such that tan(θ)=0.7\tan(\theta) = -0.7. However, since the arctangent function returns values between π/2-\pi/2 and π/2\pi/2 (or 90-90 degrees and 9090 degrees), and our vector is in the second quadrant (where both sine and cosine are negative), we need to add 180180 degrees to the arctangent value to get the correct direction angle.
  4. Find Angle in Second Quadrant: Calculating the arctangent of 0.7-0.7 using a calculator, we get θ=arctan(0.7)35.00\theta = \text{arctan}(-0.7) \approx -35.00 degrees. Since the vector is in the second quadrant, we add 180180 degrees to this value to find the actual direction angle.
  5. Calculate Final Direction Angle: Adding 180180 degrees to 35.00-35.00 degrees, we get the direction angle as 18035.00=145.00180 - 35.00 = 145.00 degrees.

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