Cos35°.cos25°/sin20°.sin10°=

[tex] \frac{cos35.cos25}{sin20.sin10} =p \\ \\ \frac{ \frac{1}{2}(cos60+cos10) }{ \frac{1}{2}(cos10-cos30) } =p \\ \\ \frac{ \frac{1}{2}+cos10 }{cos10- \frac{1}{2} \sqrt{3} } =p \\ \\ \frac{1}{2}+cos10 =p.cos10-\frac{1}{2} \sqrt{3}p \\ \\ \frac{1}{2} \sqrt{3}.p+ \frac{1}{2} =p.cos10-cos10 \\ \\ \frac{1}{2} \sqrt{3}.p+ \frac{1}{2}=(p-1).cos10 \\ \\ cos10 = \frac{\frac{1}{2} \sqrt{3}.p+ \frac{1}{2}}{p-1} [/tex]