Răspuns :
[tex] sin(\frac{\pi}{2} +x)*sinx+ cos(\frac{\pi}{2} +x)*cosx= cosx*sinx- sinx*cosx=0 [/tex]
[tex] \it Notez\ \ \dfrac{\pi}{2} +x = t,\ iar\ membrul\ st\^{a}ng\ al \ expresiei\ \ devine:
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E = sintsinx+costcosx = costcosx+sintsinx = cos(t+x) [/tex]
Revenim asupra notației :
[tex] \it E= cos\left(\dfrac{\pi}{2}+x-x\right) = cos\dfrac{\pi}{2} =0 [/tex]