Question

решите уравнение .
{x-3y=8
{x²-9y²=72

Answer 1

9(x-3y)=x^2-9y^2
9(x-3y)=(x-3y)(x+3y) 
9=x+3y 
x+3y-1=x-3y
6y=1
3y=0.5
x=8.5