- #1

jegues

- 1,097

- 3

## Homework Statement

Two vectors lie their tails at the same point. When the angle between them is increased by 20 degrees the magnitude of their vector product doubles. The original angle between them was about _____ ?

## Homework Equations

[tex]\overline{a}[/tex][tex]\bullet[/tex][tex]\overline{b}[/tex] = |[tex]\overline{a}[/tex]| |[tex]\overline{b}[/tex]| cos[tex]\theta[/tex]

## The Attempt at a Solution

Let the original angle be c and let the final angle be d, defined as follows:

d = 20 + c;

a * b = |a||b| cos(c)

a * b = 2[ |a| |b| ] cos(d)

cos(d) = cos(20 + c) = cos(20)cos(c) - sin(20)sin(c)

I get stuck about here, I can't figure it out...