In the quadrilateral given below, AB||DC, E and F are mid point of of non-parallel sides AD and BC respectively. Calculate AB, if DC=8cm and EF=9cm.
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Solution
It is given that A Quadrilateral which AB||DCAB||DC EE and FF is the mid point of non-parallel sides ADAD and BCBC To prove: (i) EFEF , if AB=6cmAB=6 cm and DC=4cmDC=4 cm (ii) ABAB , if DC=8cmDC=8 cm and EF=9cmEF=9 cm Proof: We know that The length of the segment joining the mid point of two non-parallel sides is half sum of the lengths of the parallel sides EE and FF are the midpoints of ADAD and BCBC, EF=12(AB+CD).....(1)EF=12(AB+CD).....(1) AB=6cmAB=6 cm and DC=4cmDC=4 cm Substituting in equation (1)(1) EF=182(6+4)EF=182(6+4) By further calculation EF=12×10=5cmEF=12×10=5 cm (ii) DC=8cmDC=8 cm and EF=9cmEF=9 cm Substituting equation (1) EF=12(AB+DC)EF=12(AB+DC) By further calculation 9=12(AB+8)9=12(AB+8) 18=AB+818=AB+8 So we get, 18−8=AB18−8=AB AB=10cm