A geometry problem by Aly Ahmed

Geometry Level 3

The curve above represents a parabola, it has an x x -intercept of -1 and y y -intercept of 2.


The answer is 0.25.

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1 solution

Tom Engelsman
Jun 14, 2020

Let the parabola above be represented by y = 2 ( x + 1 ) 2 . y = 2(x+1)^2. Pick a point P ( x 0 , 0 ) P(x_{0}, 0) for x 0 ( 1 , 0 ) x_{0} \in (-1,0) such that 2 ( 1 + x 0 ) 2 = x 0 . 2(1+x_{0})^2 = -x_{0}. Solving for x 0 x_{0} yields:

x 0 = 2 ( 1 + x 0 ) 2 0 = 2 x 0 2 + 5 x 0 + 2 0 = ( 2 x 0 + 1 ) ( x 0 + 2 ) x 0 = 1 2 , 2 -x_{0} = 2(1+x_{0})^2 \Rightarrow 0 = 2x_{0}^{2} + 5x_{0} + 2 \Rightarrow 0 = (2x_{0}+1)(x_{0}+2) \Rightarrow x_{0} = -\frac{1}{2}, -2 .

Since only 1 < 1 2 < 0 -1 < -\frac{1}{2} < 0 , this is the desired value we want. The square thus has an area of ( 1 2 ) 2 = 1 4 . (\frac{1}{2})^2 = \boxed{\frac{1}{4}}.

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