1)(12√13+24-45+9√13)/(5√13+10-13-2√13)=(21√13-21)/(3√13-3)=21(√13-1)/3(√13-1)=7
2)x²+5x-36=0⇒x1+x2=-5 U x1*x2=-36⇒x1=-9 U x2=4
(x³-7x²)(x²+5x-36)<0<br>x²(x-7)(x+9)(x-4)<0<br>x=0, x=7, x=-9, x=4
_ + + _ +
_______________________________________________
-9 0 4 7
x∈(-≈;-9) U (4;7)
3)2cos²x-1 +2cos5xcos2x=0
cos2x+2cos5xcos2x=0
cos2x(1+2os5x)=0
cos2x=0⇒2x=π/2+πn⇒x=π/4+πn/2
cos5x=-1/2⇒5x=+-2π/3+2πn⇒x=+-2π/15+2πn/5