How do i find the answer?
Imagine setting that vector in an xy-coordinates system- the tail of the vector is at (0, 0) and its tip is at (5, -7). Drawing a line from the tip perpendicular to the x-axis gives a right triangle where one leg has length 5 and the other leg with (signed) length -7. What is the length of the hypotenuse of that right triangle? What angle does the hypotenuse make with the x-axis?