tentukan nilai eksak dari cos 112,5

cos112,5°=−1+cos225°2−−−−−−−√cos112,5°=-1+cos225°2 hasilnya negatif, karena 112,5°112,5° di kuadran II

=−1+122√2−−−−−√=-1+1222

=−2+2√4−−−−√=-2+24

=−122+2–√−−−−−−√