Найдите tg2a ,если cosa=4/5 и 0<a<n/2

Question

Найдите tg2a ,если cosa=4/5 и 0<a<n/2

Answer 1

Sina=√1-cos²a=√1-16/25=√9/25=3/5
tga=sina/cosa=3/5:4/5=3/5*5/4=3/4
tg2a=2tga/(1-tg²a)=2*3/4:(1-9/16)=3/2:7/16=3/2*16/7=24/7

Answer 2

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