Question 1079851
 Use the characteristics of f(t) = sin t to find the value of sin t when t=-21&#960;/4 I badly need your help :-( as I dont really know how to solve this. 
here are the choices to choose from
a. sin t = 0
b. sin t = 1
c. sin t = -&#8730;2/2
d. sin t = &#8730;2/2
<pre>{{{21pi/4}}} is in the 3rd quadrant, but {{{- 21pi/4}}} is in the 2nd quadrant, and has a REFERENCE angle of {{{matrix(1,3, 3pi/4, or, 135^o)}}}. 
Thus, {{{highlight_green(matrix(1,7, - 21pi/4, "=", 3pi/4, or, sqrt(2)/2, "(CHOICE", "d.)"))}}}