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What represents the vector: 2a-5b

by imy786
Tags: 2a5b, represents, vector
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imy786
#1
Oct7-11, 01:44 PM
P: 322
1. The problem statement, all variables and given/known data

if vector :

line a starts from co-ordinates (0,0) and ends at (5,3)

line b starts from co-ordinates (0,0) and ends at (1,2)

What represents the vector: 2a-5b

2. Relevant equations



3. The attempt at a solution

I was initially thinking of computing Pythagorus theorem for each of the two lines.

for Line a = square root of (25+9) = square root of 24
for line b = square root of (1+4) = square root of 5

2a-5b = 2 x square root of 6 - 5 x square root of 5

which doesn't seem right...tips would be nice please.

need an answer in the form of an x and y co-ordinate
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LawrenceC
#2
Oct7-11, 02:05 PM
P: 1,195
Not sure of what 2a means. Does it mean a vector starting at (0,0) and ending at
(10,6)? Does 5b mean a vector starting at (0,0) and ending at (5,10)?
imy786
#3
Oct7-11, 02:25 PM
P: 322
anyone else? tips or hints?

ehild
#4
Oct7-11, 02:28 PM
HW Helper
Thanks
P: 10,670
What represents the vector: 2a-5b

2a means twice the vector a, a vector in the same line as a and of twice length. In coordinates, a=(5,3) and the vector is represented by an arrow starting at (0,0) and ending at (5,3). 2a=(10,6), 5b=(5,10)
2a-5b means the difference between 2a and 5b. When you add (subtract) vectors, you add (subtract) the components.

ehild
HallsofIvy
#5
Oct7-11, 07:30 PM
Math
Emeritus
Sci Advisor
Thanks
PF Gold
P: 39,568
Most importantly, there is nothing here that asks you to find the length of any vector. Do not use the Pythagorean theorem!
imy786
#6
Oct8-11, 08:04 AM
P: 322
so if 2a=(10,6), 5b=(5,10)

and 2a-5b

then

10-5 = 5

6-10 = -4

therefore= 2a-5b=(5,-4)
imy786
#7
Oct8-11, 08:05 AM
P: 322
thanks guys especially echild- whats your qualifications?
ehild
#8
Oct9-11, 12:59 AM
HW Helper
Thanks
P: 10,670
You are welcome.

ehild


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