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人教版初中数学七年级(下)70页第10题:要使四边形木架(用4根木条钉成)不变形,至少要再钉上几根木条?五边形木架和六边形木架呢?在教师教学用书(2007年9月第2版)中给出的答案是:要使四边形木架不变形,至少要再钉上1根木条;要使五边形木架不变形,至少要再钉上2根木条;要使六边形木架不变形,至少要再钉上3根木条.显然,在四边形木架钉上1根木条后就使其变成两个三角形,根据三角形的稳定性,能保证木架不变形
PEP junior mathematics Grade 7 (bottom) 70 pages Question 10: To make the quadrilateral wooden frame (with 4 sticks) not deformed, at least a few more wood nailed? Pentagon wooden frame and hexagons The wooden frame? The answer given in the teacher’s book (Second Edition, September 2007) is: To make the quadrilateral wooden frame not deformed, at least one more wooden strip should be nailed; the pentagonal wooden frame should not be deformed At least two more wooden strips are to be nailed; to make the hexagonal wooden frame not deformable, at least three more wooden strips must be nailed. Obviously, when a quadrilateral wooden frame nails a wooden strip, it becomes two triangles. According to the stability of the triangle, the wooden frame can not be deformed