Its the attached picture. I'm not seeing why when using the dot product, they start using sin.
Sep 14, 2013 #1 Meadman23 44 0 Its the attached picture. I'm not seeing why when using the dot product, they start using sin. Attachments untitled.JPG 8.8 KB · Views: 377 Last edited: Sep 14, 2013
Sep 14, 2013 #2 SteamKing Staff Emeritus Science Advisor Homework Helper 12,798 1,670 The picture is self explanatory. If you know trig, it should be elementary.
Sep 15, 2013 #4 Meadman23 44 0 I'm just not getting it. ' I see that the angle between r and x is phi, thus in using the formula, r (dot) x = (1)(1) cos(phi). Then I see the angle between r and y is (90-phi), thus in using the formula, r (dot) y = (1)(1)cos(90-phi) = sin (phi). I then see the angle between phi and x is (90 +phi), thus in using the formula, phi (dot) x = (1)(1)cos(90+phi) = -sin (phi) I then see the angle between phi and y is (180 - phi), thus in using the formula, phi (dot) y = (1)(1)cos(180-phi) = -cos (phi)??? I don't get why the last one is +cos(phi)....
I'm just not getting it. ' I see that the angle between r and x is phi, thus in using the formula, r (dot) x = (1)(1) cos(phi). Then I see the angle between r and y is (90-phi), thus in using the formula, r (dot) y = (1)(1)cos(90-phi) = sin (phi). I then see the angle between phi and x is (90 +phi), thus in using the formula, phi (dot) x = (1)(1)cos(90+phi) = -sin (phi) I then see the angle between phi and y is (180 - phi), thus in using the formula, phi (dot) y = (1)(1)cos(180-phi) = -cos (phi)??? I don't get why the last one is +cos(phi)....
Sep 15, 2013 #5 UltrafastPED Science Advisor Gold Member 1,912 216 Look at the blue part of the diagram ... phi(dot)y = cos(phi).