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\begin{array} { l } { \text { Ex. } 8 : \text { Prove that } } \\ { \cos ^ { 2 } \theta + \cos ^ { 2 } \left( \theta + 120 ^ { \circ } \right) + \cos ^ { 2 } \left( \theta - 120 ^ { \circ } \right) = \frac { 3 } { 2 } } \end{array} |
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