Question 1174854
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Hi
  y = -x + 49  is a function: each value of x has one value for y
vertical Line test demonstrates that.
  
{{{drawing(300,300,    -100,100,-100,100,  red(line(20,100,20,-100))  ,  
 grid(1),

graph( 300, 300, -100,100,-100,100,0, -x + 49  ))}}}

Wish You the Best in your Studies.
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