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Question

ABC is an isosceles triangle, right-angled at B. Similar triangles ACD and ABE are constructed on sides AC and AB. Find the ratio between the areas of ΔABE and ΔACD.

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Solution

Given ΔABC is an isosceles triangle in which ∠B = 90°
⇒ AB = BC
By Pythagoras theorem, we have
A C squared equals A B squared plus B C squared
A C squared equals A B squared plus A B squared[Since AB = BC]
A C squared equals 2 A B squared→ (1)
It is also given that ΔABE ~ ΔACD
Recall that ratio of areas of similar triangles is equal to the ratio of squares of their corresponding sides.
h e n c e space fraction numerator a r open parentheses increment A B E close parentheses over denominator a r open parentheses increment A C D close parentheses end fraction equals fraction numerator A B squared over denominator A C squared end fraction fraction numerator a r open parentheses increment A B E close parentheses over denominator a r open parentheses increment A C D close parentheses end fraction equals fraction numerator A B squared over denominator 2 A B squared end fraction fraction numerator a r open parentheses increment A B E close parentheses over denominator a r open parentheses increment A C D close parentheses end fraction equals 1 half
ar(ΔABE):ar(ΔACD)=1:2


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