3 Mehods:Step 1: Does the function factorise. In this case yes it does. giving y=(2x+1)(x-4)Method: Find the factors of the contract in this case (4). Which are (2,2) , (4,1)We know that a quadratic must factorise into 2 brackets (2x+/- Contant) (x+/-contant) Trial and error to find exact values. Then equalise each bracket to 0 and plot graph going through -0.5 and 4 on the x-axis. U-shape