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Mathematics 17 Online
OpenStudy (eric_d):

Chap 6.6

OpenStudy (eric_d):

Find the acute angle between the line r= 3i - 2j + lambda (i + j + k ) and x-3/2= y-2/-3= z-1/4

OpenStudy (eric_d):

@ganeshie8

ganeshie8 (ganeshie8):

angle between lines is same as the angle between their `direction vectors`

OpenStudy (factor):

ganeshie i need your help

ganeshie8 (ganeshie8):

for the first line, direction vector = i+j+k = (1, 1, 1) for the second line, direction vector = (2, -3, 4)

OpenStudy (factor):

u dere i need ur help

ganeshie8 (ganeshie8):

pm me factor

OpenStudy (factor):

okee hold a sex

ganeshie8 (ganeshie8):

find the angle between those vectors using dot product

OpenStudy (eric_d):

scalar product ?

ganeshie8 (ganeshie8):

yes a.b = |a| |b| cos(theta)

ganeshie8 (ganeshie8):

you can find angle using abvoe formula

OpenStudy (eric_d):

How do you determine this for the first line, direction vector = i+j+k = (1, 1, 1) for the second line, direction vector = (2, -3, 4)

ganeshie8 (ganeshie8):

r= 3i - 2j + lambda (i + j + k )

OpenStudy (factor):

i pm ed u

OpenStudy (eric_d):

Okay, will try now..

ganeshie8 (ganeshie8):

Notice that the direction vector is getting multiplied by a scalar `lambda` and each value of this gives you a point on the line which shoots in the direction i+j+k

ganeshie8 (ganeshie8):

in short : whatever gets multiplied by this parameter is the direction vector

OpenStudy (eric_d):

ok

ganeshie8 (ganeshie8):

a = (1,1,1) b = (2, -3, 4) your goal is to find the angle between them

OpenStudy (eric_d):

So, a.b = (1+1+1) x ( 2-3+4) ?

OpenStudy (eric_d):

I mean I can substitute them with a.b

ganeshie8 (ganeshie8):

a = (1,1,1) b = (2, -3, 4) a.b = 1*2 + 1(-3) + 1*4

ganeshie8 (ganeshie8):

set that equal to `|a| |b| cos(\theta)` and solve `\theta`

OpenStudy (eric_d):

|dw:1411727165882:dw| like this

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