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Mathematics

Find the value of:

cos2 60° + sec2 30° + tan2 45°

Trigonometric Identities

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Answer

cos260°+sec230°+tan245°=(12)2+(23)2+(1)2=14+43+1=1×34×3+4×43×4+1×1212=312+1612+1212=3+16+1212=3112=2712\text{cos}^2 60° + \text{sec}^2 30° + \text{tan}^2 45° = \Big(\dfrac{1}{2}\Big)^2 + \Big(\dfrac{2}{\sqrt3}\Big)^2 + (1)^2\\[1em] = \dfrac{1}{4} + \dfrac{4}{3} + 1\\[1em] = \dfrac{1 \times 3}{4 \times 3} + \dfrac{4 \times 4}{3 \times 4} + \dfrac{1 \times 12}{12}\\[1em] = \dfrac{3}{12} + \dfrac{16}{12} + \dfrac{12}{12}\\[1em] = \dfrac{3 + 16 + 12}{12}\\[1em] = \dfrac{31}{12}\\[1em] = 2\dfrac{7}{12}

Hence, cos2 60° + sec2 30° + tan2 45° = 27122\dfrac{7}{12}.

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