Ctg(arccos(-1/3))=1/tg(arccos(-1/3))=1/tg(П+argtg(√(1-1/9)/(-1/3)))=1/tg(arctg((√8/9)/(-1/3)))=-√2/4;
sin(2arccos1/4)=2sin(arccos1/4)cos(arccos1/4)=2*1/4*sin(arcsin√(1-1/16))=1/2*√154=√15/8
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(36+216×6+2×6²)×6⁻³
(36+1296+2×36)×6⁻³
(36+1296+72)×6⁻³
1404×6⁻³
39×6²×6⁻³
36×6⁻³
≈6,5
Решение в скрине.
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