Question

cos^3$\alpha$-sin^3$\alpha$
если cos$\alpha$-sin$\alpha$=0.2

Answer 1

cos³a-sin³a =?
сosa-sina=0.2 возведем все во 2 степень
 cos²a-2sinacosa+sin²a= 0.04
1-2sincosa= 0.04
2sincosa=0.96  
cos³a-sin³a = (cos-sina)(cos+sin)(cos+sin) 
=0.96 ( sina+cosa)² =0.96(sin²a+2sincosa+cos²a)=0.96(1+0.96)= 1.8816
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думаю так