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20 16 Fengxian Mathematical Module 2
(1) connecting BG, EG, BD, ∫e, g are midpoint respectively, ∴EG∥AB and EG=AB,

∴ quadrilateral ABGE is a parallelogram, ∴AE∥BG,

∠DGB is the angle formed by straight lines in different planes?

The side length of the cube is 1, DG = 52, BG = 52, DB = 2,

∴cos∠DGB= 15

The angle of a straight line on different planes is arccos 15. ..

(2) in: cubic ABCD-a1b1c1d1,∴BC⊥ surface EGC.

∴BC is the height of the triangular pyramid B-C 1CE,

∴VB 1? C 1CE= 13? SC 1CE? BC = 13× 12× 1× 1× 1 = 16。