Задача 57495 ...

5f3ea7e3faf909182968ddd9

28.01.2021 19:28:58

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По формулам:
[r]cos α *cos β =(1/2)cos( α + β )+(1/2)cos( α - β )[/r]
[r]sinα *sin β =(1/2)cos( α - β )-(1/2)cos( α +β )[/r]

(1/2)cos(4+6)+(1/2)cos(4-6)-(1/2)cos(1-3)+(1/2)cos(1+3)=

=(1/2)cos(7+3)+(1/2)cos(7-3)

[b](1/2)cos(10)[/b]+(1/2)cos(-2)-(1/2)cos(-2)+[u](1/2)cos(4)[/u]=[b](1/2)cos(10)[/b]+[u](1/2)cos(4)[/u]- верно