\(E=\)\(cos^273+1-sin^247+cos73\left(cos120.cos73+sin120.sin73\right)\)
\(=cos^273+1-\left(sin120.cos73-cos120.sin73\right)^2-\dfrac{1}{2}.cos^273+\dfrac{\sqrt{3}}{2}cos73.sin73\)
\(=cos^273+1-\left(\dfrac{\sqrt{3}}{2}.cos73+\dfrac{1}{2}.sin73\right)^2-\dfrac{1}{2}.cos73^2+\dfrac{\sqrt{3}}{2}cos73.sin73\)
\(=\dfrac{1}{2}cos^273+1-\left(\dfrac{3}{4}cos^273+\dfrac{\sqrt{3}}{2}.cos73.sin73+\dfrac{1}{4}sin^273\right)+\dfrac{\sqrt{3}}{2}.cos73.sin73\)
\(=1-\dfrac{1}{4}.cos^273-\dfrac{1}{4}.sin^273\)
\(=1-\dfrac{1}{4}=\dfrac{3}{4}\)
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