0=c
40=a×400+b×20+c
0=a×900+b×30+c
A=- 1/5, b=6 and c=0 can be obtained by solving the equation.
The functional relationship between y 1 and t is y 1 =- 1/5x 2+6x, 0≤t≤30.
The relationship between y2 and t can be obtained from fig. 2 as follows:
╭2x (0≤x