@book{15,
	author = {Weir, Maurice D. and Hass, Joel},
	title = {Thomas Calculus},
	publisher = {Pearson education,},
	year = {2008.},
	address = {Chennai :},
	edition = {11th ed.},
	url = {https://books.google.com.pk/books?id=ps8zduMZW5AC&printsec=frontcover&dq=thomas+calculus+11th+edition&hl=en&sa=X&ved=2ahUKEwjTqNi--qH2AhVMzIUKHZoTA4UQ6AF6BAgJEAI#v=onepage&q=thomas%20calculus%2011th%20edition&f=false}
}