Question

若tana=1/3,则sin^3 a+2cos^ 3 a/sin^3 a-2cos^3 a

Answer 1

分子分母同除以cos^3a

(sin^3 a+2cos^ 3 a)/(sin^3 a-2cos^3 a)

=(sin³a/cos³a+2)/(sin³a/cos³a-2)

=(tan³a+2)/(tan³a-2)

=[(1/3)³+2]/[(1/3)³-2]

=(1+2*27)/(1-2*27)

=-55/53