列方程解应用题,既是初中代数的重点,又是难点,而设“未知数”x,又是解应用题的难点.因此,掌握“未知数”x的设法,对解应用题尤为重要.本文略举数例向同学们说明如何设“未知数”x,请看: 一、直接设元 例1 某汽车司机计划用7小时将某种物资运往280千米以外的某地,司机用每小时40千米的速度行驶了2.5小时后,接上级指示要提前1.5小时到达.问司机需改用每小时多少千米的速度行驶? 解;设司机需改用的速度为x千米/小时,则用x The application of the column equation solution is not only the focal point but also the difficult point of the algebra of junior middle school. Setting the “unknown number” x is also a difficult point to solve the application problem. Therefore, it is very important to master the “unknown number” x and solve the application problem. To give a few examples to the students explaining how to set the “unknown number” x, see: 1. Directly setting example 1 A car driver plans to transport a certain material to a location 280 kilometers away for a period of 7 hours. The driver uses 40 thousand kilometers per hour. After 2.5 meters of speed traveled, the higher order instructions arrived 1.5 hours ahead of schedule. Ask the driver to switch to the speed of kilometers per hour. Solution: Set the speed of the driver to switch to x km/h. x