在投针试验中,若l=5cm,a=20cm,则针与平行线相交的概率约为______.
针和平行线相交概率的计算公式P=2lπa=2×520π≈0.159.
故答案为:0.519.
He _________ English for eight years by the time he graduates from the university next year.
A.will learn
B.will have learned
C.will be learning
D.has graduated
读六大板块示意图,回答下列问题。
(1)板块名称:
A:______,B:______,C:______,D:______,E:______,F:______.
(2)六大板块中,几乎全部是海洋的是______板块。
(3)日本多火山地震,是因为日本处于______板块与______板块的交界地带,板块相互碰撞而形成。