A) \[{{100}^{o}}\]and \[{{260}^{o}}\]
B) \[{{80}^{o}}\]and\[{{280}^{o}}\]
C) \[{{280}^{o}}\]and \[{{110}^{o}}\]
D) \[{{110}^{o}}\]and \[{{260}^{o}}\]
Correct Answer: A
Solution :
Here \[\cos \theta =1-2{{\cos }^{2}}{{40}^{o}}\] = \[-(2{{\cos }^{2}}{{40}^{o}}-1)\] \[=-\cos (2\times {{40}^{o}})\]= \[-\cos {{80}^{o}}\] = \[\cos ({{180}^{o}}+{{80}^{o}})=\cos ({{180}^{o}}-{{80}^{o}})\] Hence, \[\cos 260{}^\circ \text{and}\cos 100{}^\circ \] i.e., \[\theta =100{}^\circ \] and 260°.
You need to login to perform this action.
You will be redirected in
3 sec
