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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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Review exercises 7 255

EXERCISES7.7

1 If

⎛ ⎞

1

1

a =

⎜0

⎝1

1

⎛ ⎞

3

2

and b=

⎜1

⎝0

1

findthe norm ofa, the norm ofband a·b.Further,

findthe norm ofa −b.

2 Two non-zero vectors are mutually orthogonal iftheir

scalar product iszero. Determine which ofthe

following are mutually orthogonal.

⎛ ⎞ ⎛ ⎞ ⎛ ⎞

1 2 3

a = ⎜ 2

⎝ 4 ⎠ b = ⎜1

⎝0

⎠ c = ⎜0

⎝1

−1 0 0

⎛ ⎞ ⎛ ⎞

0 3

d = ⎜0

⎝7

⎠ e = ⎜ 0

⎝ −2 ⎠

2 −5

Solutions

1 2, √ 15,6, √ 7 2 aande,bandd

REVIEWEXERCISES7

1 Finda·banda×bwhen

(a) a=7i−j+k,b=3i+2j+5k

(b) a=6i−6j−6k,b=i−j−k.

2 Foratriangle ABC, express assimplyaspossiblethe

vector → AB + → BC + → CA.

3 Ifa=7i−j+2kandb=8i+j+k,find|a|,|b|and

a ·b. Deducethe cosineofthe anglebetweenaand b.

4 Ifa=6i−j+2kandb=3i−j+3k,find

|a|,|b|, |a ×b|.Deducethe sineofthe anglebetween

aandb.

5 Ifa=7i+9j−3kandb=2i−4j,findâ, ˆb, ̂ a×b.

6 Bycombining the scalar andvector productsother

types ofproductscan be defined. The triplescalar

productforthreevectors isdefined as (a ×b)·c

whichisascalar.Ifa=3i−j+2k,b=2i−2j−k,

c=3i+j,finda×band(a×b)·c.Showthat

(a×b)·c=a·(b×c).

7 Thetriplevectorproduct isdefined by (a ×b) ×c.

Find the triple vectorproduct ofthe vectors given in

Question6. Alsofind a ·c,b·c andverifythat

(a·c)b−(b·c)a=(a×b)×c

Further,finda × (b ×c) andconfirm that

a×(b×c)≠(a×b)×c.

8 Show thatthe vectorsp = 3i −2j +k,

q=2i+j−4kandr=i−3j+5kformthethree

sides ofaright-angledtriangle.

9 Find aunitvector parallelto the liney = 7x −3.Find

a unitvector paralleltoy = 2x +7.Use the scalar

product to findthe anglebetweenthese two lines.

10 An electric chargeqwhichmoves with avelocity v

produces amagnetic fieldBgiven by

B = µq v× ˆr

4π |r| 2 where µ = constant

FindBifr=3i+j−2kandv=i−2j+3k.

11 InatriangleABC, denote → ABbyc, → AC byband → CB

by a.Usethe scalar product to provethe cosine rule:

a 2 =b 2 +c 2 −2bccosA.

12 Evaluate

ij k

(a)

−4 0 −3

∣ 71 4 ∣

(b)

i jk

825

∣100∣

13 Find the area ofthe parallelogram with sides

representedby3i +5j −k and i +3j −k.

14 Find the anglebetween the vectors 7i +2j and i −3j.

15 Find aunitvector in the directionofthe linejoining

the points (2,3,4) and (7,17,1).

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