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Given that f ′′ ( x ) = cos ( x ) f ″ ( x ) = cos ⁡ ( x ) , f ′ ( π / 2 ) = 7 f ′ ( π / 2 ) = 7 and f ( π / 2 ) = 5 f ( π / 2 ) = 5 find: f ′ ( x ) = f ′ ( x ) = f ( x ) = f ( x ) =

Sagot :

Answer: [tex]\sin x+6[/tex]

[tex]-\cos x+6x+5-3\pi[/tex]

Step-by-step explanation:

Given

[tex]f''(x)=\cos x[/tex]

Integrating the equation

[tex]\Rightarrow f''(x)=\dfrac{d^2y}{dx^2}=\cos x\\\\\Rightarrow \int \frac{\mathrm{d^2} y}{\mathrm{d} x^2}=\int \cos x\\\\\Rightarrow \frac{\mathrm{d} y}{\mathrm{d} x}=\sin x+c[/tex]

Put [tex]x=\frac{\pi}{2}\ \text{and}\ \frac{dy}{dx}=7[/tex]

[tex]\Rightarrow 7=\sin \frac{\pi }{2}+c\\\Rightarrow c=7-1\\\Rightarrow c=6[/tex]

[tex]\Rightarrow \dfrac{dy}{dx}=\sin x+6[/tex]

again integrating both sides of the equation

[tex]\Rightarrow \int \frac{\mathrm{d} y}{\mathrm{d} x}=\int (\sin x+6)dx\\\\\Rightarrow y=-\cos x+6x+c_1[/tex]

Put  [tex]x=\frac{\pi}{2}\ \text{and}\ y=5[/tex]

[tex]\Rightarrow 5=-\cos \frac{\pi}{2}+6(\frac{\pi}{2})+c_1\\\Rightarrow c_1=5-3\pi[/tex]

[tex]\therefore f(x)=y=-\cos x+6x+5-3\pi[/tex]