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The first function application problem in junior two mathematics
As we all know, the distance between A and B is 90 kilometers. Xiaoming rides a bike from A to B, and his average speed is15 km/h. 。

(1) Find the analytic function of the distance y (unit: km) from Xiaoming to terminal B and the departure time x (unit: h). Is y a linear function of x?

(2) Find the range of the independent variable x..

Solution: y is a linear function about x,

The analytical formula is y=90- 15x,

The range of independent variables is 0.

The length of a high-quality mosquito-repellent incense is 105cm, and it is observed that the length of the hour is shortened by 10cm after the small sea is ignited.

(1) Write the functional relationship between the length y(cm) of mosquito-repellent incense after ignition and the ignition time t(h);

(2) How long can mosquito-repellent incense last?

Solution: The functional relationship is: y = 105- 10h (0

When the mosquito-repellent incense is ignited, that is, when y=0,

105- 10h=0

The solution is h= 10.5.

That is, mosquito-repellent incense can be used for 10.5 hours.