1.

In a right triangle the square of the hypotenuse is equal to the sum of the squares of the other two sides ?prove we are given a right triangle ABC right angled at B.

Answer»

Given: A right triangle ABC right angled at B.

To Prove: AC2 = AB2 + BC2

Construction: Draw BD ⊥ AC

Proof:

In Δ ADB and Δ ABC,

∠ ADB = ∠ ABC (each 90°)

∠ BAD = ∠ CAB (common)



Δ ADB ~ Δ ABC (By AA similarity criterion)

Now, AD/AB = AB/AC (corresponding sides are PROPORTIONAL)

AB2 = AD × AC … (i)

SIMILARLY, Δ BDC ~ Δ ABC

BC2 = CD × AC … (II)

ADDING (i) and (ii)

AB2 + BC2 = (AD × AC) + (CD × AC)

AB2 + BC2 = AC × (AD + CD)

AB2 + BC2 = AC2

Hence Proved.


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