InparallelogramBSNL,BS=LN&BS∥LN.IfBS∥LN&BNisthetransversalthen∠LNK=∠SBK{Alternateangles}IfBS∥LN&SListhetransversalthen∠KLN=∠KSB{Alternateangles}In△LKN&△SKB,∠LNK=∠SBKBS=LN∠KLN=∠KSBSo△LKN≅△SKB{ByASARuleofCongruency}SoKL=SKGivenKL=7cm⇒LS=2KL=2×7=14cmInarectanglebothdiagonalsareequal,soBN=LS=14cm