# Homework Help: Need to solve thise 2 equations

1. May 2, 2010

### weedannycool

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

i have 2 equations:

400cos $$\vartheta$$a = 300 + Vacos45

and

400sin $$\vartheta$$a = Vasin45

2. Relevant equations

3. The attempt at a solution

i have no clue, maybe square it.

thanks

2. May 2, 2010

### tiny-tim

Hi weedannycool!
Yes, of course …

what do you get?

3. May 2, 2010

### Staff: Mentor

Also, you should replace cos45 and sin45 by sqrt(2)/2. I'm assuming the angles are in degrees.

One other thing. Instead of starting a new thread for essentially the same (but corrected) problem, you should continue the old thread, putting in the corrected set of equations.

4. May 3, 2010

### weedannycool

right so i have the to equations squared. not positive with what i should to next though. is there a method for solving these.

thanks for the help so far

5. May 3, 2010

### Staff: Mentor

Do you know any identities involving the sum of the squares of the sine and cosine functions?

6. May 3, 2010

### RTW69

Mark44's approach replacing sin45 and cos45 with sqrt(2)/2 seems the most straight forward approach. You have 2 equations with 2 unknowns, theta-a and Va. The expression with Va*sqrt(2)/2 in the second equation can be substituted into the first equation. You are left with one equation with one unknown, theta-a. Trial and error to find theta-a. Plug theta-a into either equation to find Va. Theta-a will be in degrees, Va won't be.

7. May 3, 2010

### weedannycool

thanks guys. relative motion is a blast.