1. ctg 15 градусов — tg 15 Градусов=… .? 2. cos^4 (5pi/12) — sin^4 (5pi/12)=…?

1. ctg 15 — tg 15=cos15/sin15 — sin15/cos15=(cos^2 15 — sin^2 15) / (sin15*cos15)=cos30/sin15*cos15=sqrt (3) / (2sin15*cos15)=sqrt (3) / sin30=sqrt (3) / 1/2=2sqrt (3) 2. cos^4 (5pi/12) — sin^4 (5pi/12)=(cos^2 (5pi/12) — sin^2 (5pi/12) (cos^2 (5pi/12)+sin^2 (5pi/12)=(cos (5pi/6)*1=-sqrt (3) /2