Question

sin(arccos1/4)=?

Answer 1

令 x =arccos (1/4),

则 x ∈(0,π),

且 cos x =1/4.

所以 sin x =√ [ 1 -(cos x)^2 ]

= √15 /4.

即 sin [ arccos (1/4) ] = √15 /4.

= = = = = = = = =

换元法.

注意 f(u) =arccos u 的值域.

arccos