Найдите tg a, если 3 sin^2 a + 8 cos^2 a=4

3 sin^2 a +8 cos^2 a = 4;
3 sin^2 a + 8cos^2 a = 4(sin^2 a + cos^2 a);
3sin^2 a + 8cos^2  = 4 sin^2 a + 4 cos^2 a;
 sin^2 a= 4 cos^2 a;  /:cos^2 a ≠ 0;
tg^2 a = 4;
tga = 2 
tg a = - 2