七册P.99关于三角形的内角和是180°的第三个实验是:把三角形的三个角沿虚线折过去,三个角正好组成一个平角.(注意带点的字).按照这个说法做实验,教师示范必须预先画好虛线,不便当场演示.学生实验时,也必须辅导他们先画好虚线图,不便于独立操作.而且,三段虚线中的水平虚线,实质上是三角形的中位线,也不便于学生理解.为了便于学生操作,我认为这个实验可以作些改进.先画底边上的高,再将三角形的顶点向垂足折过 P.99 The third experiment on the interior angle of a triangle, which is 180 °, is to fold the three corners of the triangle along a dotted line, and the three corners form exactly one (see the dotted words). To do the experiment, the teacher demonstration must draw a dotted line in advance, which is inconvenient for the on-the-spot demonstration. Students also must instruct them to paint the dotted line diagram first, which is inconvenient for independent operation. Moreover, the horizontal dotted line in the three dotted line is essentially a triangle In order to facilitate the operation of students, I think this experiment can make some improvements. Draw the bottom of the high, then the vertex of the triangle fold down to the foot