B1. {y=2x–4
{x^2+3(2x–4)–15=0
x^2+6x–12–15=0
x^2+6x–27=0
Д=/36–4•1•(-27)=/144=12
х1=(-6+12)/2=3
х2=(-6-12)/2=-9
у1=2•3–4=2
у2=2•(-9)–4=–22
Ответ: (3;2) и (-9;-22)
В2. {х=5–2у
{(у–х)/ху=1/2
у–х=0,5ху
у–5+2у=0,5у(5–2у)
3у–5=2,5у–у^2
у^2+0,5у–5=0
Д=/0,25–4•1•(-5)=/20,25=4,5
у1=(-0,5+4,5)/2=2
у2=(-0,5-4,5)/2=-2,5
х1=5–2•2=1
х2=5–2•(-2,5)=10
Ответ: (1;2) и (10;-2,5)