71/15*31/13-41/15*31/13
выносим 31/13
31/13*(71/15-41/15)=
31/13*2=62/13=4 целые 10/13
3sin2x+8cos²x=7
3*2sinxcosx+8cos²x=7*(sin²x+cos²x)
cos²x+6sinxcosx-7sin²x=0 (делим обе части на cos²x):
-7tg²x+6tgx+1=0
tgx=y=>-7y²+6y+1=0=>y1=1;y2=-1/7
1)tgx=1=>x=pi/4+pin
<span>2)tgx=-1/7=>x=-arctg(1/7)+pik,n,k-целые.</span>
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<span>Ответ. 4*x + y =-3; -y - x^2 = 6; x^2-4*x+3=0; (x-1)*(x-3)=0; x1=1; x2=3; y1=7; y2=-15;</span>