Question

1.若3sin a + 4cos a =0 ,则 tan 2a

Answer 1

(1)3sin a + 4cos a =0

--> tan a=-4/3

--> tan 2a=2tan a/(1-(tan a)^2)=2*(-4/3)/(1-16/9)=24/7

(2)

sin2a =2*sina *cosa= A

(sin a - cos a)^2

=1-2sina*cosa

=1-A

因为:a∈ (0 ,π/4 )

--> tan a sina sina - cosa