Объяснение:
а)sinα/2=±√(1-cosα)/2, α/2∈1 четв. sinα/2=+√(1+12/13)/2=
√25/26=5/√26.
б)tg2α=2tgα/(1-tg²α), ctg2α=1/tg2α
tgα=sinα/cosα=+√1-144/ 169 :(-12/13)=5/13: (-12/13)= - 5/12.
tg2α=2·(-5/12):(1-25/144)= -5/6: 119/144= -120/119.
ctg2α=- 119/120.
