http://ww.math.msu.edu/webwork2_files/tmp/equations/c1/ccbbe29241b71ca0e9bc9e5267276f1.png
http://ww.math.msu.edu/webwork2_files/tmp/equations/c1/ccbbe29241b71ca0e9bc9e5267276f1.png
http://ww.math.msu.edu/webwork2_files/tmp/equations/c1/ccbbe29241b71ca0e9bc9e5267276f1.png