1.
a=-1+2+6 =>a=7
b=1-2 =>b=-1
(a+b)/2 = (7-1)/2 = 3
2.
0,8(3)=(83-8)/90=75/90=5/6
x/y=5/6 =>5y=6x =>x=5y/6
(5y/6 + 2y)/(2y - 5y/6)=
(5y+12y)/(12y-5y)=
17y/7y=
17/7
3.
4+5y-4=0 =>5y=0 =>y=0
4.
[tex] \sqrt{9- \sqrt{80} } = \sqrt{ \frac{9+ \sqrt{81-80} }{2} } - \sqrt{ \frac{9- \sqrt{81-80} }{2} } = \sqrt{5} -2[/tex]
√(3-√5+√5-2)=√1=1
5.
A_____B_________________C
40 cm
AB/AC=1/5 =>AC=5AB
AC=AB+BC
5AB=AB+40
4AB=40 =>AB=10 cm =>AC=50 cm
6.
Daca MN ll BC =>AM/AB=AN/AC=3/5 =>3AC=5AN =>AC=5AN/3
AC=AN+NC
5AN/3 = AN + NC lx3
5AN=3AN+3NC
2AN=3NC =>AN/NC=3/2
