Question

Зная,что sint=4/5, π/2≤t≤π ,вычислите cos(π/6+t)

Answer 1

cost=-√1-sin²t=-√1-16/25=-√9/25=-3/5
cos(π/6+t)=cosπ/6cost-sinπ/6sint=√3/2*(-3/5)-1/2*4/5=-3√3/10-4/10=-(3√3+4)/10