Q. Find the direction angle of u=(−7,−10). Enter your answer as an angle in degrees between 0∘ and 360∘ rounded to the nearest hundredth.
Understand Direction Angle: Understand the concept of a direction angle.The direction angle of a vector in the plane is the angle measured counterclockwise from the positive x-axis to the vector. For a vector u=(x,y), the direction angle θ can be found using the arctangent function, where θ=arctan(xy). However, since the arctangent function only gives values from −2π to 2π, we need to adjust the angle depending on the quadrant in which the vector lies.
Identify Vector Quadrant: Identify the quadrant in which the vector lies.The vector u=(−7,−10) lies in the third quadrant because both x and y are negative. In the third quadrant, the direction angle is between 180∘ and 270∘.
Calculate Arctangent: Calculate the arctangent of the vector's y-coordinate divided by its x-coordinate. θ=arctan(xy)=arctan(−7−10)=arctan(710). We use a calculator to find the arctangent of 710.
Adjust for Third Quadrant: Adjust the angle for the third quadrant.Since the arctangent function gives us an angle in the first quadrant, we need to add 180∘ to get the direction angle in the third quadrant.θ=arctan(710)+180∘.
Calculate Exact Direction Angle: Calculate the exact value of the direction angle.Using a calculator, we find that arctan(710)≈55.00∘ (rounded to two decimal places).Therefore, θ≈55.00∘+180∘=235.00∘.
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