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Date May 2019 Marks available 7 Reference code 19M.1.SL.TZ1.S_6
Level Standard Level Paper Paper 1 Time zone Time zone 1
Command term Find Question number S_6 Adapted from N/A

Question

The magnitudes of two vectors, u and v, are 4 and 33 respectively. The angle between u and v is π6π6.

Let w = u − v. Find the magnitude of w.

Markscheme

* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.

METHOD 1 (cosine rule)

diagram including u, v and included angle of π6π6      (M1)

eg   

sketch of triangle with w (does not need to be to scale)      (A1)

eg  

choosing cosine rule      (M1)

eg    a2+b22abcosCa2+b22abcosC

correct substitution        A1

eg   42+(3)22(4)(3)cosπ642+(3)22(4)(3)cosπ6

cosπ6=32cosπ6=32 (seen anywhere)       (A1)

correct working        (A1)

eg    16 + 3 − 12

| w | = 77        A1    N2

 

METHOD 2 (scalar product)

valid approach, in terms of u and v (seen anywhere)      (M1)

eg   | w |2 = (u − v)•(u − v), | w |2 = u− 2uvv, | w |= (u1v1)2+(u2v2)2(u1v1)2+(u2v2)2,

| w | = (u1v1)2+(u2v2)2+(u3v3)2(u1v1)2+(u2v2)2+(u3v3)2

correct value for uu (seen anywhere)       (A1)

eg   | u|2 = 16,  uu = 16,  u12+u22=16u12+u22=16

correct value for vv (seen anywhere)      (A1)

eg  | v|2 = 16,  vv = 3,  v12+v22+v32=3v12+v22+v32=3

cos(π6)=32cos(π6)=32  (seen anywhere)      (A1)

uv =4×3×32=4×3×32  (= 6)  (seen anywhere)       A1

correct substitution into u− 2uvv or u12+u22+v12+v222(u1v1+u2v2)u12+u22+v12+v222(u1v1+u2v2)  (2 or 3 dimensions)      (A1)

eg   16 − 2(6) + 3  (= 7)

| w | = 77        A1    N2

Examiners report

[N/A]

Syllabus sections

Topic 3—Geometry and trigonometry » AHL 3.13—Scalar and vector products
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Topic 3—Geometry and trigonometry

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