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\(∵ \sin⁡ 17°=\cfrac{x}{y}\)
বা, \(\sin^2⁡ 17°=(\cfrac{x}{y})^2\)
বা, \(1- \sin^2⁡ 17° =1-\cfrac{x^2}{y^2}\)
বা, \(\cos^2⁡ 17°=\cfrac{y^2-x^2}{y^2}\)
বা, \(\cos⁡ 17°=\sqrt{\cfrac{y^2-x^2}{y^2}}\)
বা, \(\cos⁡ 17°=\cfrac{\sqrt{y^2-x^2}}{y}\)

\(\sec⁡ 17°-\sin⁡ 73°\)
\(=\cfrac{1}{\cos⁡ 17°} -\sin⁡(90°-17°)\)
\(=\cfrac{1}{\cos⁡ 17°} -\cos⁡ 17°\)
\(=\cfrac{1}{\cfrac{\sqrt{y^2-x^2}}{y}}-\cfrac{\sqrt{y^2-x^2}}{y}\)
\(=\cfrac{y}{\sqrt{y^2-x^2}}–\cfrac{\sqrt{y^2-x^2}}{y}\)
\(=\cfrac{y^2-(y^2-x^2 )}{y\sqrt{y^2-x^2}}\)
\(=\cfrac{y^2-y^2+x^2}{y\sqrt{y^2-x^2}}\)
\(=\cfrac{x^2}{y\sqrt{y^2-x^2}}\) (প্রমাণিত)