***************************************************************************************
(a+b)²-(a-b)²=
=(a+b-(a-b))*(a+b+a-b)=
=(a+b-a+b)*2a=
=2b*2a=
=4ab
***************************************************************************************
(x+3)*(x-2)-3(x-4)=
=x²-2x+3x-6-3x+12=
=x²-2x+6
***************************************************************************************
X³-27=x³-3³=(x-3)(x²+3x+9)
(√32+√98-√50) /√72 = (4√2+7√2-5√2) / 6√2=6√2 / 6√2 = 1
..............................................................................................
{4х+у=-10
{5х-2у=-19
4х+у=-10
у=-10-4х
5х-2у=-19
5х-2*(-10-4х)=-19
5х+20+8х=-19
13х=-19-20
13х=-39
х=-39:13
х=-3
у=-10-4х
у=-10-4*(-3)
у=-10+12
у=2
Ответ: х=-3, у=2