I need help! Can someone help me with this problem?

1. Apr 19, 2007

princiebebe57

What is the length of the resultant vector of combining 2A - 3B where vector A= 4i + 3j and vector B= 9i + 8j?

2. Apr 19, 2007

J77

First thing is to multiply the vectors by the given amounts... post your result.

3. Apr 19, 2007

princiebebe57

is it -19i + 30j?

4. Apr 19, 2007

J77

No, what's 2A and 3B?

5. Apr 19, 2007

princiebebe57

2A = 8i + 6j
3B = 27i + 24j

is that correct???

6. Apr 19, 2007

J77

Yep -- now do the subtraction.

7. Apr 19, 2007

princiebebe57

so (8i + 6j)-(27i + 24j)?

8. Apr 19, 2007

J77

Yeah. What's it equal?

9. Apr 19, 2007

princiebebe57

is it -19i - 18j?

10. Apr 19, 2007

J77

Yeah -- and the length (magnitude) is...

11. Apr 19, 2007

princiebebe57

i'm stuck at that!

12. Apr 19, 2007

cristo

Staff Emeritus
The magnitude of a vector $x\vec{i}+y\vec{j}=\sqrt{x^2+y^2}$. So, what does give you in your case?

Last edited: Apr 19, 2007
13. Apr 19, 2007

princiebebe57

so is it 26.172?

14. Apr 19, 2007

J77

Yep -- to 3 decimal places.

15. Apr 19, 2007

princiebebe57

Thank you so much!!

16. Apr 19, 2007

Edgardo

Hello princiebebe57,

you may find this website here interesting. It contains some questions and answers on vectors.
If you want to remember the formula for the length of a vector, it helps thinking of the Pythagorean theorem.

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