Toán Lớp 9: sin25+cos70/sin20+cos65(có độ mỗi số nha )
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Toán Lớp 9: sin25+cos70/sin20+cos65(có độ mỗi số nha )
Comments ( 2 )
\dfrac{{\sin {{25}^o} + \cos {{70}^o}}}{{\sin {{20}^o} + \cos {{65}^o}}} = \dfrac{{\sin \left( {{{90}^o} – {{65}^o}} \right) + \cos \left( {{{90}^o} – {{20}^o}} \right)}}{{\sin {{20}^o} + \cos {{65}^o}}}\\
= \dfrac{{\cos {{65}^o} + \sin {{20}^o}}}{{\sin {{20}^o} + \cos {{65}^o}}} = 1
\end{array}$