Question 440021
(1) {{{ x + 2y + 4z = 12 }}}
(2) {{{ y + 2z = 8 }}}
(3) {{{ 5y = 10 }}}
There are 3 equations and 3 unknowns, so it's solvable
(2) {{{ y + 2z = 8 }}}
(2) {{{ 2z = -y + 8 }}}
(2) {{{ z = (-1/2)*y + 4 }}}
Substitute this into (1)
(1) {{{ x + 2y + 4*((-1/2)*y + 4) = 12 }}}
(1) {{{ x + 2y - 2y + 16 = 12 }}}
(1) {{{ x = -4 }}}
and
(3) {{{ 5y = 10 }}}
(3) {{{ y = 2 }}}
and
(2) {{{ z = (-1/2)*y + 4 }}}
(2) {{{ z = (-1/2)*2 + 4 }}}
(2) {{{ z = -1 + 4 }}}
(2) {{{ z = 3 }}}