-5(0,6c-1,2)-1,5c-3 = -3c+6-1,5c-3 = -4,5c+3 = -4,5×(-4,9)+3 = 22,05+3 = 25,05.
1)
(√75-√12)*2√3=(5√3-2√3)*2√3=30-12=18
2)
(2√5-√20)*√5=(2√5-2√5)*√5=0*√5=0
5*1/2(дробь)=5/2(дробь)=2,5
{xy=6
{2x-y=11
{y=2x-11
{x(2x-11)=6
x(2x-11)=6
2x²-11x-6=0
D=121+48=169=13²
x₁=(11+13)/4=6
x₂=(11-13)/4=-0.5
x=6⇒y=2*6-11=1
x=-0.5⇒y=2*(-0.5)-11=-12
Ответ: (6;1), (-0.5;-12)