Total revenue is defined as the total sale proceeds of a producer by selling corresponding level of output therefore total revenue can be defined as the total sales proceed of the seller by selling the number of units at a given price.

In a perfectly competitive market the firm is a price taker so it can't influence the price hence it can change its total revenue by changing the quantity of output sold.

TR = P X Q

Where,

TR - Total Revenue

Q - Quantity of Output sold

P - Price

The total revenue curve is give below –

It touches the X-axis because the TR is zero if zero output is sold.