Question

sin^2a+2sinacosa-3cos^2a= -3,则tana的值?

Answer 1

sin^2a+2sinacosa-3cos^2a= -3

即 -(cos^2a-sin^2a)+2sinacosa-(2cos^2a-1)+2=0

即 -cos2a+sin2a-cos2a+2=0

即 sin2a-2cos2a+2=0

即 2tga/(1+tg^2a)-2(1-tg^2a)/(1+tg^2a)+2=0

即 2tg^2a+tga=0

即 tga(2tga+1)=0

所以 tga=0 或 tga=-1/2