Toán Lớp 9: Help mik voi a:
4. Tính các tổng sau:
sin30° + sin60°; cos60° + cos30°, sin60° + cos30°
sin30° + sin60° + cos45°.
5. a) Biết sin48° 0,7431. Tìm sin42°.
b) Biết cos44° 0,7193. Tìm cos46
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Toán Lớp 9: Help mik voi a:
4. Tính các tổng sau:
sin30° + sin60°; cos60° + cos30°, sin60° + cos30°
sin30° + sin60° + cos45°.
5. a) Biết sin48° 0,7431. Tìm sin42°.
b) Biết cos44° 0,7193. Tìm cos46
Comments ( 1 )
4)\sin {30^0} + \sin {60^0}\\
= \dfrac{1}{2} + \dfrac{{\sqrt 3 }}{2} = \dfrac{{1 + \sqrt 3 }}{2}\\
\cos {60^0} + \cos {30^0} = \dfrac{1}{2} + \dfrac{{\sqrt 3 }}{2} = \dfrac{{1 + \sqrt 3 }}{2}\\
\sin {60^0} + \cos {30^0} = \dfrac{{\sqrt 3 }}{2} + \dfrac{{\sqrt 3 }}{2} = \sqrt 3 \\
\sin {30^0} + \sin {60^0} + \cos {45^0}\\
= \dfrac{1}{2} + \dfrac{{\sqrt 3 }}{2} + \dfrac{{\sqrt 2 }}{2}\\
= \dfrac{{1 + \sqrt 3 + \sqrt 2 }}{2}\\
5)a)\sin {42^0} = \cos \left( {{{90}^0} – {{42}^0}} \right)\\
= \cos {48^0}\\
= \sqrt {1 – {{\sin }^2}{{48}^0}} \\
= \sqrt {1 – 0,{{7431}^2}} \\
= 0,669\\
b)\cos {46^0} = \sin \left( {{{90}^0} – {{46}^0}} \right)\\
= \sin {44^0}\\
= \sqrt {1 – {{\cos }^2}{{44}^0}} \\
= 0,695
\end{array}$