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Prove that two triangles having the same base (or equal bases) have equal areas between the same parallels.

Answer
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Hint: Assume two triangles between two parallel lines having the same base. We know the formula of the area of the triangle, Area=12×Base×Height . We also know the property that the distance between parallel lines is always constant. So, each perpendicular distance between the parallel lines is always equal to each other. Now, solve it further.

Complete step-by-step answer:
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Assume two line segments AB and CD parallel to each other and two triangles which are ΔFEG and ΔHEG having the same base EG.
Let the distance between the parallel lines AB and CD be x.
In ΔFEG , we have,
EG as the base of the ΔFEG ,
FI is the height which is also perpendicular to the base EG.
We know the formula of the area of the triangle,
Area=12×Base×Height
Now, using this formula to get the area of the ΔFEG .
Area of ΔFEG = 12×EG×FI ………………………..(1)
In ΔHEG , we have,
EG as the base of the ΔHEG ,
HJ is the height which is also perpendicular to the base EG.
We know the formula of the area of the triangle,
Area=12×Base×Height
Now, using this formula to get the area of the ΔHEG .
Area of ΔHEG = 12×EG×HJ ………………..(2)
We know the property that the distance between parallel lines is always constant. So, each perpendicular distance between the parallel lines is always equal to each other.
Using this property, we can say that,
FI=HJ ………..(3)
From equation (2), and equation (3), we get
Area of ΔHEG = 12×EG×FI ………………..(4)
From equation (1), we have
Area of ΔFEG = 12×EG×FI .
Now, we can say that equation (1) and equation (4) are equal to each other.
So, Area of ΔHEG= Area of ΔFEG .
Therefore, two triangles having the same base (or equal bases) have equal areas between the same parallels.
Hence, proved.
Note: In this question, one may think to use heron’s formula for the area of the triangle. That is, Area=s(sa)(sb)(sc) . But if we use this formula, then we will not be able to use the property of parallel lines, and also this formula will make our solution complex to solve. Therefore, don’t think to use heron’s formula here.
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