\(sin51°=\cfrac{a}{\sqrt{a^2+b^2}}\) হলে, tan51°+tan39° এর মান কত?
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\(sin51° = \cfrac{a}{ \sqrt {a^2 +b^2}}\)
বা, \(sin^251° = \cfrac{a^2}{ a^2 +b^2}\)
বা, \(1-sin^251° = 1-\cfrac{a^2}{ a^2 +b^2}\)
বা, \(cos^251° =\cfrac{a^2+b^2-a^2}{ a^2 +b^2}\)
বা, \(cos51° =\sqrt{\cfrac{b^2}{ a^2 +b^2}}=\cfrac{b}{\sqrt{a^2+b^2}}\)

\(\therefore tan51°=\cfrac{sin51°}{cos 51°}\)
\(=\cfrac{\cfrac{a}{ \sqrt {a^2 +b^2}}}{\cfrac{b}{ \sqrt {a^2 +b^2}}}\)
\(=\cfrac{a}{b}\)

এবং \(cot 51°=\cfrac{1}{tan 51°}=\cfrac{b}{a}\)

\(tan51°+tan39°\)
\(=tan51°+tan(90°-51°)\)
\(=tan 51°+cot51°\)
\(=\cfrac{a}{b}+\cfrac{b}{a}\)
\(=\cfrac{a^2+b^2}{ab}\) [Answer]

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