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Let AB = 4. Extend AB to C so that BC = 12ab. D is the midpoint of AC, and extend AB to e reversely so that EA = ad. find the length of AE
As shown in the figure: ∵ line AB = 4cm, BC = 12ab, ∵ BC = 2cm, ∵ AC = 4 + 2 = 6cm, ∵ D is the midpoint of AC, ∵ ad = 3cm, ∵ EA = ad. ∵ AE = 3cm
If the midpoint of AB, BC and ad is known to be C, D and e respectively, then AE is equal to the midpoint of ab
Let BD = X
Then CD = x, ad = 3x, ab = 4x, AE = 1.5x
∴AE/AB=1.5/4=3/8
That is, AE is 3 / 8 of ab
Given the line segment AB, take its midpoint C, then draw the midpoint D of BC, then draw the midpoint e of AD, then AE is equal to ()
A、1/3 B、2/5 C、3/7 D、3/8
D
Given the vector a = (2,4), B = (1,1), if the vector B ⊥ (a + λ b), then the value of real number λ is______ ．
A + λ B = (2,4) + λ (1,1) = (2 + λ, 4 + λ). ∵ B ⊥ (a + λ b), ∵ B · (a + λ b) = 0, that is, (1,1) · (2 + λ, 4 + λ) = 2 + λ + 4 + λ = 6 + 2 λ = 0, ∵ λ = - 3
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