Question 490314

you are given the system:

{{{3x+9y=12}}}........1

{{{5x-4y=3}}}........2
---------------------------..take one equation and solve it for one unknown variable (either {{{x}}} or {{{y}}})


{{{3x+9y=12}}}........1...I will solve this one for {{{y}}}


{{{9y=-3x+12}}}


{{{9y/9=-3x/9+12/9}}}


{{{y=-(1/3)x+4/3}}}....now, I will substitute {{{y}}} in equation 2


{{{5x-4(-(1/3)x+4/3)=3}}}........2


{{{5x+(4/3)x-16/3=3}}}

{{{5x*3+3(4/3)x-16*3/3=3*3}}}


{{{15x+4x-5.33=9}}}


{{{19x=9+5.33}}}


{{{19x=14.33}}}


{{{x=14.33/19}}}


{{{highlight(x=0.75)}}}


now find {{{y}}}


{{{y=-(1/3)0.75+4/3}}}


{{{y=-0.25+1.33}}}

{{{highlight(y=1.08)}}}


check:

{{{3x+9y=12}}}........1

{{{3(0.75)+9(1.08)=12}}}

{{{2.25+9.72=12}}}

{{{11.97=12}}}

{{{12=12}}}