6cosx+5sinx=0

Question

6cosx+5sinx=0

Answer 1

5(2cos²x-1)-2cosx-3=0 10cos²x-2cosx-8=0 Замена а=cosx, 10а²-2а-8=0 5а²-а-4=0 D=1+80=9² a1=(1-9)/20=-8/20=-2/5=-0.4 a2=(1+9)/20=1/2 x=±arccos(-0.4)+2πn, n∈Z; x=±π/3+2πn, n∈Z;