[填空题]
The graph below shows the amount of ;,xe0alyrl9 ybcc jg5j bc:wzs9v 21ob4hs -;money M (in thousands of dollars), in the a7 kd k;x8ghig *qw+*xhccount of a contractor, where t is the t;h h8*xk*gg+qkix7 dw ime in months since he opened the account.
1.Write down one characteristic of the graph which suggests that a cubic function might be an appropriate model for the amount of money in the account.The equation of the model can be expressed as M(t)=$at^3$+$bt^2$+$ct$+$d$, where a, b, c and d∈R. It is given that the graph of the model passes through the following points.
2.(1)State the value of d.
(2)Using the values in the table, write down three equations in a, b, and c.
(3)By solving the system of equations from part (ii), find the values of a, b and c. a = b = c =
If M has a negative value, the contractor is in debt.
3.Use the model from part (b) to find the number of months the contractor expects to be in debt. Give your answer to the nearest month.
