Найти значение выражения 6tga*sin (π-a) если cosa=0.3

Tg (a) = sin (a) / cos (a),

sin (pi-a) = sin (a),

sin^2 (a) = 1-cos^2 (a):

6tg (a) * sin (pi-a) =

=6 (sin (a) / cos (a)) * sin (a) =

=6sin^2 (a) / cos (a) =

=6 (1-cos^2 (a)) / cos (a)

↓

6 (1-0,3^2) / 0,3=

=6 (0,91) / 0,3=

=20*0,91=

=18,2.