Помогите решить пожалуйста

1. $3*(\frac{1}{3}):2-19*\frac{1}{3}=3*\frac{1}{9}-\frac{19}{3}=\frac{1}{3}-\frac{19}{3}= \frac{1-19}{3}=- \frac{18}{3}=-6$
2. $\frac{a^2-4}{4a^2}*\frac{2a}{a+2}=\frac{(a-2)(a+2)}{2a}*\frac{1}{a+2}=\frac{a-2}{2a}$
   $\frac{0.5-2}{2*0.5}=\frac{-1.5}{1}=-1.5$
3. $2\sqrt{50a}-4\sqrt{2a}+\sqrt{2a}=2*5\sqrt{2a}-4\sqrt{2a}+\sqrt{2a}=10\sqrt{2a}-4\sqrt{2a}+\sqrt{2a}=7\sqrt{2a}$
4. $2x^2+5x-12=0$
   $D=b^2-4ac=5^2-4*2*(-12)=25+96=121$
   $\left \{ {{x=\frac{-5+11}{4} } \atop {x=\frac{-5-11}{4}}} \right.$
   $\left \{ {{x=1.5} \atop {x=-4}} \right.$
5. $\left \{ {{y-5-3x=-3} \atop {y=-5x+10}} \right.$
   $-5x+10-5-3x=-3$
   $x=1$
   $\left \{ {{x=1} \atop {y=-5*1+10}} \right.$
   $\left \{ {{x=1} \atop {y=5}} \right.$