Смотри /////////////////////////////
(x+y)/2+(x-y)/3=6 |*6
(x+y)/4-(x-у)/3=6 |*12
3(x+y)+2(x-y)=36
3(x+y)-4(x-у)=72
3х+3у+2х-2у=36
3х+3у-4х+4у=72
5х+у=36
-х+7у=72
у=36-5х
-х+7(36-5х)=72
-х+252-35х=72
-36х=72-252
-36х=-180
х=-180:(-36)
х=5
у=36-5х
у=36-5*5=36-25=11
Ответ: х=5; у=11
A) x^2+16x+63=
=b^2-4ac=256-252=4
x1,=(-16+2)÷2=-7
x2=(-16-2)÷2=-9
(х-1)(х+1)(х^2+1)(х^4+1)=х^8-1
(х^2-1)(х^2+1)(х^4+1) = (х^4-1)(х^4+1) = х^8-1
х^8-1 = х^8 - 1