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August08
a fost răspuns

Aratati ca sin x+ rad(3)*cos x<=2 , oricare x apartine R

Răspuns :

[tex]sinx+\sqrt3cosx \leq 2[/tex]


[tex]f(x) = sinx+\sqrt3cosx[/tex]

[tex]f'(x) = 0 => -\sqrt3sinx+cosx=0[/tex]

[tex]-\sqrt3sinx=-cosx | (-1) => \sqrt3sinx=cosx | :cosx[/tex]

[tex]\sqrt3tgx=1 => tgx = \frac{1}{\sqrt3}[/tex]

[tex]x=\frac{\pi}{6}; \frac{7\pi}{6}[/tex]


[tex]f''(x) = -\sqrt3cosx-sinx[/tex]

[tex]f''(\frac{\pi}{6}) = -\sqrt3\frac{\sqrt3}{2} -\frac{1}{2} < 0 =>[/tex] f are maxim la [tex]x = \frac{\pi}{6}[/tex]

Valoarea maxima pentru [tex]f(\frac{\pi}{6}) = \sqrt3* \frac{\sqrt3}{2} + \frac{1}{2} = 2[/tex]

1*sinx+√3cosx≤2 | impartim toata relatia cu 2

(1/2) *sinx+(√3/2) * cosx≤1

cos(π/3)sinx+sin(π/3)cosx≤1

sin(x+π/3)≤1

fie α=x+π/3

-1≤sinα≤1, adevarat ∀α∈R⇒adevarat ∀x=α-π/3