Question

cum verific aceasta egalitate?
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Answer 1

a. aplicam formula

$sin(a+b)=sin a\times cosb+sinb\times cosa\\\\sin(90+x)=sin90\times cosx+sinx\times cos90=cosx$

Precizam ca : sin90=1 si cos90=0

b. aplicam formula

$cos(a+b)=cosa\times cosb-sina\times sinb\\\\cos(90+x)=cos90\times cosx-sin90\times sinx=0-sinx=-sinx$