In △ABC, AB=AC
Thus, ∠B=∠C (I) (angles opposite to equal sides are equal)
In △BEC and △BFC
⇒∠E=∠F=90o ...(Given)
⇒BC=BC ...(common side)
⇒∠ABC=∠ACB ...(From I)
Thus, △BEC≅△BFC ....(SAA test of Congruency)
Hence, BF=CE
Given, AB=AC
⇒AB−BF=AC−CE
⇒AF=AE