-7у +15= -2у -5
-7у+2у=-5-15
-5у=-20
у= -20: (-5)
у= 4
-13= -13
1,2x-(1.5+3.4x)=1.2x-1.5-3.4x=-2.2x-1.5
1) 29\8 * [ 53\12 - 3\2 + 0.75) * 4/7} = 29\8 * 44\21 = 319\42 = 7.595
Х²-у=72
х+у=9
у=9-x
х²- (9-x) =72
х²-9+x -72 =0
х²+х -81=0
D= 1²- 4(-81) = 1+324=325
D>0 - два корня
x₁= (-1+5√13 )/2
x₂= (-1- 5√13) /2
y₁ =9- (-1+5√13)/2 = (18-(-1+5√13))/2=(19-5√13)/2
y₂= 9 - (-1-5√13)/2 = (18-(-1-5√13))/2= (19+5√13)/2