Sunday, August 31, 2008

`u = , v = ` Find the angle theta between the vectors.

You need to use the formula of dot product to find the angle between two vectors, `u = u_x*i + u_y*j, v = v_x*i + v_y*j` , such that:


`u*v = |u|*|v|*cos(theta)`


The angle between the vectors u and v is theta.


`cos theta = (u*v)/(|u|*|v|)`


First, you need to evaluate the product of the vectors u and v, such that:


`u*v = u_x*v_x + u_y*v_y`


`u*v = 3*4 + 2*(0)`


`u*v = 12`


You need to evaluate the magnitudes |u| and |v|, such that:


`|u|= sqrt(u_x^2 + u_y^2) => |u|= sqrt(3^2 + 2^2) =>|u|= sqrt13 `


`|v|= sqrt(v_x^2 + v_y^2) => |v|= sqrt(4^2 + 0^2) => |v|= 4`


`cos theta = (12)/(4sqrt13) => cos theta = (3)/(sqrt13)`


Hence, the cosine of the angle between the vectors u and v is `cos theta = (3)/(sqrt13)` , so, `theta ~~ 34^o.`

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