Question
In a $\triangle ABC , \angle B =35^{\circ}$ and $\angle C =55^{\circ}$. Write which of the following is true:
  1. $A C^2=A B^2+B C^2$
  2. $A B^2=B C^2+A C^2$
  3. $B C^2=A B^2+A C^2$

Answer



In $\triangle\text{ABC}, $
$\angle\text{B}= 35^\circ$ and $\angle\text{C}= 55^\circ$
$\Rightarrow\angle\text{A}= 180^\circ-(\angle\text{B} + \angle\text{C})$
$\Rightarrow\angle\text{A}= 180^\circ-(35^\circ + 55^\circ)$
$\Rightarrow\angle\text{A}= 180^\circ-90^\circ$
$\angle\text{A}= 90^\circ$
By Pythagoras Theorem,
$BC^2=AB^2+ AC^2$
(iii) is true.

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