multivariable functions, domains, ranges of graphs, level curves level surfaces definitions multivariable functions domains outputs graphs level curves level surfaces defintions part 1 multivariable functions domains outputs graphs level curves level surfaces defintions part 2 multivariable functions domains outputs graphs level curves level surfaces defintions part 3 multivariable functions domains outputs graphs level curves level surfaces defintions part 4 multivariable functions domains outputs graphs level curves level surfaces defintions part 5 multivariable functions domains ranges graphs level curves level surfaces defintions part 6 multivariable functions domains ranges graphs level curves level surfaces defintions part 7 multivariable functions domains ranges graphs level curves level surfaces defintions part 9 multivariable functions domains ranges graphs level curves level surfaces defintions part 10 multivariable functions domains ranges graphs level curves level surfaces defintions part 12