MHB How Do You Find the Length x in a Geometric Problem with Shaded Areas?

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To find the length x in the geometric problem with a shaded area of 1200 cm², the areas of a triangle and rectangle are considered. The triangle's area is initially set up as A_triangle = (1/2)(x-1)(x), but it is corrected to A_triangle = (1/2)x². The equation combining both areas is A_rectangle + A_triangle = 2400, leading to the equation (1/2)x² + x = 1200. Solving this quadratic equation yields x = 48 cm as the valid solution. The final answer is x = 48 cm.
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Find the length x if the shaded area is 1200 cm^2

I tried to solve this is what I get

since $A_{triangle}=(\frac{1}{2})({x-1})(x)$

and $A_{rectangle}=x$

$A_{rectangle}+A_{triangle}=2400$

Is the set-up of my equation correct?
 

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Why are you using $x-1$ in the area of the triangle?
 
MarkFL said:
Why are you using $x-1$ in the area of the triangle?

I see it. $A_{TRI}=\frac{1}{2}(x^2)$

now I will have

$\frac{1}{2}(x^2)+x=2400$

solving for x $(x-48)(x+50)=0$

$x=48 in.$ :D
 
Well, you actually have:

$$\frac{1}{2}x^2+x=1200$$

or:

$$x^2+2x-2400=0$$

$$(x+50)(x-48)=0$$

Discarding the negative root, we then find:

$$x=48\text{ cm}$$
 
Here is a little puzzle from the book 100 Geometric Games by Pierre Berloquin. The side of a small square is one meter long and the side of a larger square one and a half meters long. One vertex of the large square is at the center of the small square. The side of the large square cuts two sides of the small square into one- third parts and two-thirds parts. What is the area where the squares overlap?

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