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 Main Question or Discussion Point 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: 309 Last edited: Sep 14, 2013
Main Question or Discussion Point Its the attached picture. I'm not seeing why when using the dot product, they start using sin.
Related General Math News on Phys.org Scientists develop method to help epidemiologists map spread of COVID-19 Solution to century-old math problem could predict transmission of infectious diseases Mathematician helps resolve question first asked 60 years ago
Related General Math News on Phys.org Scientists develop method to help epidemiologists map spread of COVID-19 Solution to century-old math problem could predict transmission of infectious diseases Mathematician helps resolve question first asked 60 years ago
Sep 14, 2013 #2 SteamKing Staff Emeritus Science Advisor Homework Helper 12,798 1,666 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).