a) 1−sin2α; b) (1−cosα)(1+cosα); c) 1+sin2α+cos2α; d) sinα−sinα.cos2α;
2 câu trả lời
Bạn tham khảo!
$\text{a) 1-Sin²$\alpha$}$
$\text{Có Sin²$\alpha$+Cos²$\alpha$=1}$
$\rightarrow$ $\text{Cos²$\alpha$=1-Sin²$\alpha$}$
$\text{b) (1-Cos$\alpha$)(1+Cos$\alpha$)}$
⇔$\text{1-Cos²$\alpha$}$
⇔$\text{Sin²$\alpha$}$
$\text{c) 1+Sin²$\alpha$+Cos²$\alpha$}$
⇔$\text{1+1}$
⇔$\text{2}$
$\text{d) Sin$\alpha$-Sin$\alpha$.Cos²$\alpha$}$
⇔$\text{Sin$\alpha$(1-Cos²$\alpha$)}$
⇔$\text{Sin$\alpha$.Sin²$\alpha$}$
⇔$\text{Sin³$\alpha$}$
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