Ratios are proportional if they represent the same relationship. One way to see if two ratios are proportional is to write them as fractions and then reduce them. If the reduced fractions are the same, your ratios are proportional.
Answer:

Step-by-step explanation:
The diagonals of a rectangle always bisect each other. Therefore, we can set
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When x=0 y=50 when y=0 x=+\-5. -x^2 makes the parabola open downward y(x)=2x^2+50;y(3)=2*9+50=32