Eitan is on a train heading west into the city while Dmitri is on a train on the adjacent track heading east, away from the city
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Let us assume uniform width = x cm wide.
Length of rectangular portrait = 50cm and width of rectangular portrait = 70cm.
Therefore, length of rectangle made by frame = 50 + x+x = (2x+50) cm.
And width of rectangle made by frame = 70+x+x = (2x+70) cm.
We know, the area of rectangular portrait = 50 × 70 = 3500 cm^2.
Total area of the rectangle made by frame would be = (2x+50) * (2x+70)
We know,
Actual area of frame = Area of rectangle made by frame - area of rectangular portrait.
We also given "the area of the frame is the same as the area of the portrait."
We can setup an equation now,
3500 = (2x+50) * (2x+70) - 3500.
Subtracting 3500 from both sides, we get
3500-3500 = (2x+50) * (2x+70) - 3500-3500.
0 = (2x+50) * (2x+70) -7000.
FOIL (2x+50) * (2x+70), we get
0 = 2x*2x +2x*70 + 50*2x +50*70 - 7000.
0 = 4x^2 +140x +100x +3500 -7000.
4x^2 +240x -3500 = 0.
Dividing whole equation by 4, we get
x^2 +60x - 875 =0
Applying quadratic formula , we get
We cant take negative value.
So,
We could take approximately 12 cm.