Given a sine, cosine, or tangent value, find the principle angle who has this value. In other words, find the arcsine, arccosine, or arctangent of that value.


The following are all angle measures (in radians, rounded to the nearest hundredth) whose tangent is minus, 21.
Which is the principal value of tangent, start superscript, minus, 1, end superscript, left parenthesis, minus, 21, right parenthesis?
Please choose from one of the following options.