1)sin^2x+3sinx*cosx-4cos^2x=0 /(cos^2x) sin^2x/cos^2x+3sinxcosx/cos^2x-4cos^2x/cos^2x=0 tg^2x+3tgx-4=0 d=9+4*4=25 vd=5 tgx=-3+-5/2 tgx=1 tgx=-4
x=pi/4+pi*n x2=arctg(-4)+pi*m n,m (-Z
2)2cos5x*cos8x-cos13x=0 2*cos(5x+8x)+cos(5x-8x)/2-cos13x=0 cos13x+cos(-3x)-cos13x=0 cos(-3x)=0 (-3x)=pi/2+pi*n x=-pi/6-pi/3*n n(-Z
3)2lgx-lg(x+3)=lg2 lgx^2-lg(x+3)=lg2 lg(x^2/(x+3))=lg2 x^2/(x+3)-2=0 x^2-2x-6=0
d=4+12=16 vd=4 x1=2-4/2=-1 x2=2+4/2=3 одз x.>0 x+3>0 x>-3=>x>0 и х1=-1 не уд одз ответ х2=3
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