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Re: In square ABCD, E is a point on side CD. [#permalink]
Expert Reply
The key to solving this problem lies in the formula for the area of a triangle:

$$
\(\text { Area }=\frac{1}{2} \times \text { Base × Height }\)
$$

1. Define the Square's Dimensions

Let the side length of the square $\(A B C D\)$ be $\(s\)$.
- The Area of the Square $\(=s \times s=s^2\)$.
- The side $A B$ is parallel to the side $C D$.
- The side $A D$ is parallel to the side $B C$.
- The length of $\(A B=s\)$.

2. Calculate the Area of the Shaded Region (Quantity A)

The shaded region is Triangle $A B E$.
- Base: We can use side $A B$ as the base. Thus, Base $=A B=s$.
- Height: The height of the triangle must be the perpendicular distance from the vertex $E$ to the line containing the base $A B$. Since $A B C D$ is a square and $E$ is on $C D$, this perpendicular distance is equal to the side length of the square, $A D$ or $B C$, which is $s$.

$$
\(\begin{gathered}
\text { Area of Shaded Region }=\text { Area of } \triangle A B E=\frac{1}{2} \times \operatorname{Base}(A B) \times \text { Height } \\
\text { Area of Shaded Region }=\frac{1}{2} \times s \times s=\frac{1}{2} s^2
\end{gathered}\)
$$

3. Calculate the Area of the Unshaded Region (Quantity B)

The unshaded region is everything in the square that is not shaded.

Area of Unshaded Region $=$ Area of Square $A B C D-$ Area of Shaded Region

Area of Unshaded Region $\(=s^2-\frac{1}{2} s^2=\frac{1}{2} s^2\)$

(Alternatively, the unshaded region is composed of two triangles: $\(\triangle B C E\)$ and $\(\triangle A D E\)$.

$\(\operatorname{Area}(\triangle B C E)=\frac{1}{2} \times B C \times C E\)$ and $\(\operatorname{Area}(\triangle A D E)=\frac{1}{2} \times A D \times D E\)$. Since $\(A D= B C=s\)$ and $\(C E+D E=s\)$, the total area is: $\(\frac{1}{2} s(C E+D E)=\frac{1}{2} s(s)=\frac{1}{2} s^2\)$.)

Since the area of the shaded triangle $A B E$ is exactly half the area of the square, and the unshaded area is the other half, the two quantities are equal.

Therefore, the relationship is The two quantities are equal.
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Re: In square ABCD, E is a point on side CD. [#permalink]
Expert Reply
grefighter888 wrote:
Carcass wrote:
OE

Let us draw a perpendicular from E which intersects AB at F.

Attachment:
GRE square (3).jpg



Since ABCD is a square, EF divides it into two rectangles BCEF and FEDA.
As we know that a diagonal divides the rectangle into two equal areas.

So, BE being a diagonal of BCEF divides it in two equal regions, say X.
Similarly, AD being a diagonal of FEDA divides it into two equal regions, say Y.

Attachment:
GRe square 2.jpg




Area of the shaded region X + Y

Area of the unshaded region X + Y

C is the answer



but could E, any other points on the line? E is not always the midpoint that we can divide into 2 rectangles. or it doesn't have to be mid point and the answer is still C?
Carcass



let me know if still unclear
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Re: In square ABCD, E is a point on side CD. [#permalink]
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