Toán cos2 20độ+ cos2 40độ+ cos2 50độ +cos2 70độ 13/09/2021 By Josie cos2 20độ+ cos2 40độ+ cos2 50độ +cos2 70độ
$cos^{2}$ $20^{o}$ + $cos^{2}$ $40^{o}$+ $cos^{2}$ $50^{o}$+$cos^{2}$ $70^{o}$ = $cos^{2}$ $20^{o}$ + $cos^{2}$ $40^{o}$ $sin^{2}$ $40^{o}$+ $sin^{2}$ $20^{o}$ = ($cos^{2}$ $20^{o}$ + $sin^{2}$ $20^{o}$) + ( $cos^{2}$ $40^{o}$ $sin^{2}$ $40^{o}$) = 1 + 1 = 2 Trả lời
$cos^{2}$ $20^{o}$ + $cos^{2}$ $40^{o}$+ $cos^{2}$ $50^{o}$+$cos^{2}$ $70^{o}$
= $cos^{2}$ $20^{o}$ + $cos^{2}$ $40^{o}$ $sin^{2}$ $40^{o}$+ $sin^{2}$ $20^{o}$
= ($cos^{2}$ $20^{o}$ + $sin^{2}$ $20^{o}$) + ( $cos^{2}$ $40^{o}$ $sin^{2}$ $40^{o}$)
= 1 + 1
= 2
Đáp án:
Giải thích các bước giải: 161