# Simple trigonometry check

1. Nov 5, 2009

### hanelliot

1. The problem statement, all variables and given/known data
a = 1/sqrt(29) * (-2*sint, 0, -2*cost)
length of a is?

2. Relevant equations

3. The attempt at a solution
ignoring 0, we have sqrt{[(-2*sint)/sqrt(29)]^2 + [(-2*cost)/sqrt(29)]^2}. I get 2/sqrt(29) but answer is [2*sqrt(2)]/sqrt(29). Can anyone do this step by step and show me please..

2. Nov 5, 2009

### HallsofIvy

Staff Emeritus
No need to. You answer is correct. $2\sqrt{2}/\sqrt{29}$ would be $\sqrt{4+ 4}/\sqrt{29}$ but $4sin^2(t)+ 4cos^2(t)= 4$ not 4+ 4.

3. Nov 5, 2009

### hanelliot

hmm so solution must be wrong.. I wonder why no one pointed it out tho