math common core hsf.tf.c.8 unit circle radians hsf.tf.a.2 degrees identities quadrants reciprocal half angle formulas f.tf.4 pre-calculus phase shift vertical shift period f.tf.6 algebra hsf.tf.a.3 common srt functions 30-60-90 45-45-90 hsf.tf.c.9 reference angles pythagorean identity co-function identity f.tf.3 sohcahtoa transformations hsg.srt.c.6 amplitude