Chapter 1 - Systems of Linear Equations - 1.1 Introduction to Systems of Linear Equations - 1.1 Exercises - Page 10: 39

$u=40; v=40$

$2u+v=120$ $u+2v=120$ $(u+2v)-2v=(120)-2v$ $u=-2v+120$ $2(-2v+120)+v=120$ $-4v+240+v=120$ $-3v+240=120$ $(-3v+240)-240=(120)-240$ $-3v=-120$ $(-3v)\div-3=(-120)\div-3$ $v=40$ $2u+(40)=120$ $(2u+(40))-40=(120)-40$ $2u=80$ $(2u)\div2=(80)\div2$ $u=40$ $2(40)+(40)=120$ $80+40=120$ $120=120$ $(40)+2(40)=120$ $40+80=120$ $120=120$