Trigonometry Problem: Finding Length of Vector a = (-2sint, 0, -2cost)

[hanelliot]

Homework Statement

a = 1/sqrt(29) * (-2*sint, 0, -2*cost)
length of a is?

Homework Equations

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..

 

[HallsofIvy]

Homework Statement

a = 1/sqrt(29) * (-2*sint, 0, -2*cost)
length of a is?

Homework Equations

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..

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.

 

[hanelliot]

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