## anonymous one year ago Quick check? Thank You for helping! Use the formula v1*v2=|v1||v2|cos theta to find the cosine of the angle between the two vectors (-7,8) and (5,3). I got cos theta=-11/61.97. Is this correct? Thanks!

1. anonymous

@nincompoop @Michele_Laino @ganeshie8 @campbell_st @zepdrix @Luigi0210 @Destinymasha @radar @Whitemonsterbunny17

2. anonymous

I also solved for theta, getting 100.22 degrees.

3. Michele_Laino

we can write this: $\left\| {{v_1}} \right\| = \sqrt {49 + 64} = 10.63$ $\left\| {{v_2}} \right\| = \sqrt {25 + 9} = 5.83$ ${v_1} \cdot {v_2} = - 35 + 24 = - 11$ so we get: $\cos \theta = \frac{{ - 11}}{{10.63 \times 5.83}}$

4. anonymous

so same thing, awesome!

5. anonymous

Thanks for the confirmation!

6. Michele_Laino

yes! $\cos \theta = \frac{{ - 11}}{{10.63 \times 5.83}} = - \frac{{11}}{{61.97}}$

7. Michele_Laino

:)