Question 188025
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Given;
x= 4y + 7, EQN 1
7x + y= 20, EQN 2


Substitute EQN 1 in EQN 2:
{{{7(highlight(4y+7))+y=20}}}
{{{28y+49+y=20}}}
{{{29y=20-49=-29}}}---->{{{cross(29)y/cross(29)=cross(-29)1/cross(29)}}}
{{{red(y=-1)}}}, substitue in EQN 1
{{{x=4(-1)+7=-4+7=red(3)}}}
Answer (x,y)=<font color=red>(3,-1)</font>


We'll see graph:
{{{drawing(400,400,-5,8,-5,5,grid(1),graph(400,400,-5,8,-5,5,(x-7)/4,20-7x),blue(circle(3,-1,.12)))}}}==> RED, EQN 1 ;; GREEN, EQN 2


Thank you,
Jojo</font>