Question

1 求sin10sin50sin70的值 2：若tan(π|4-α）=3,则cotα等于

Answer 1

1 .sin10sin50sin70=cos10sin10sin50sin70/cos10

=[1/2(sin20cos20cos40)]/cos10

=(1/4sin40cos400/cos10

=(1/8sin80)/cos10

=1/8

2 .tan-α=tan[(π|4-α）-π|4]=[tan(π|4-α）-tan(π|4）]/1+tan(π|4-α)

=1/2

所以tanα=-1/2

cotα等于1/tanα=-2