lec-3https://www.slideshare.net/upload?download_id=53486085&original_file=true&_gl=1*2btg42*_gcl_au*MTI1NDQwNDgxOC4.pptx lec-3https://www.slideshare.net/upload?download_id=53486085&original_file=true&_gl=1*2btg42*_gcl_au*MTI1NDQwNDgxOC4xNzY4MDQxMTk1.pptx 
