# Homework Help: How to solve an equation

1. Mar 17, 2012

### TheronSimon

1. The problem statement, all variables and given/known data

(V2-V1)^2 = 552+452-2*55*45*cos135

= 92.5m/s

My question is how to get from the first equation to the answer...

2. Mar 17, 2012

### emailanmol

552+452-2*55*45*cos135

Is not solved correctly.
It doesnt come up to 92.5(assuming the calculation you were working on didn't need change of units.

3. Mar 17, 2012

### TheronSimon

its something from the course material, so i guess its just wrong....

4. Mar 17, 2012

### emailanmol

Yeah, it sounds like wrong.
If you can perhaps add some back ground context we may be able to work out what the text wanted to convey :-)

5. Mar 17, 2012

### Staff: Mentor

Looks suspiciously like an application of the cosine law where the exponents have lost their superscipt. Thus:

$x^2 = 55^2 + 45^2 - 2\cdot55\cdot45\cdot cos(135°)$

solve for x.

6. Mar 17, 2012

### TheronSimon

haha! there we go thanks! i guess it it was just a typo in the course material.

7. Mar 17, 2012

### emailanmol

OMG!
How did i miss that!
That was incredible observation gneill

8. Mar 17, 2012

### Staff: Mentor

I attribute it to to many hours doing math and not enough enjoying St. Patrick's day parties. I shall have to make amends

9. Mar 17, 2012

### jey1234

I agree. Remarkable

10. Mar 17, 2012

### PeterO

What is supposed to be 92.5 m/s

V2, V1 or the difference V2 - V1 ?