In the given Fig. DEFG is a square and ∠BAC = 90°. Prove that
(i) ∆AGF ~ ∆DBG.
(ii) ∆AGF ~ ∆EFC.
(iii) ∆DBG ~ ∆AEFC
(iv) DE2 = BD × EC.
In ∆DCF and ∆EAD
∠2 = ∠4 [corresponding angles]
and    ∠1 = ∠3 [corresponding angles]
Therefore, by using AA similar condition
             Â
      Â
       Â
      Â
        ...(i)   Â
[Taking reciprocals of both sides]
Now, in ∆EAD and ∆EBF
∠4 = ∠4    [common]
and    ∠3 = ∠1 [corresponding angles]
Therefore, by using AA similar condition
              Â
        Â
      Â
Comparing (i) and (ii), we get