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Let 
f(x)=2cos((x)/(2)).
Find 
f^('')(x).
Choose 1 answer:
(A) 
-cos((x)/(2))
B 
-sin((x)/(2))
(C) 
-8cos((x)/(2))
(D) 
-(1)/(2)cos((x)/(2))

Let f(x)=2cos(x2) f(x)=2 \cos \left(\frac{x}{2}\right) .\newlineFind f(x) f^{\prime \prime}(x) .\newlineChoose 11 answer:\newline(A) cos(x2) -\cos \left(\frac{x}{2}\right) \newline(B) sin(x2) -\sin \left(\frac{x}{2}\right) \newline(C) 8cos(x2) -8 \cos \left(\frac{x}{2}\right) \newline(D) 12cos(x2) -\frac{1}{2} \cos \left(\frac{x}{2}\right)

Full solution

Q. Let f(x)=2cos(x2) f(x)=2 \cos \left(\frac{x}{2}\right) .\newlineFind f(x) f^{\prime \prime}(x) .\newlineChoose 11 answer:\newline(A) cos(x2) -\cos \left(\frac{x}{2}\right) \newline(B) sin(x2) -\sin \left(\frac{x}{2}\right) \newline(C) 8cos(x2) -8 \cos \left(\frac{x}{2}\right) \newline(D) 12cos(x2) -\frac{1}{2} \cos \left(\frac{x}{2}\right)
  1. Differentiate function f(x)f(x): Differentiate the function f(x)=2cos(x2)f(x) = 2\cos(\frac{x}{2}) with respect to xx to find the first derivative f(x)f'(x). Using the chain rule, the derivative of cos(u)\cos(u) with respect to xx is sin(u)-\sin(u) times the derivative of uu with respect to xx. Here, u=x2u = \frac{x}{2}, so the derivative of uu with respect to xx is f(x)=2cos(x2)f(x) = 2\cos(\frac{x}{2})22. f(x)=2cos(x2)f(x) = 2\cos(\frac{x}{2})33
  2. Simplify first derivative: Simplify the expression for the first derivative. f(x)=sin(x2)f'(x) = -\sin(\frac{x}{2})
  3. Differentiate f(x)f'(x): Differentiate the first derivative f(x)=sin(x2)f'(x) = -\sin(\frac{x}{2}) with respect to xx to find the second derivative f(x)f''(x). Using the chain rule again, the derivative of sin(u)-\sin(u) with respect to xx is cos(u)-\cos(u) times the derivative of uu with respect to xx. Here, u=x2u = \frac{x}{2}, so the derivative of uu with respect to xx is f(x)=sin(x2)f'(x) = -\sin(\frac{x}{2})22. f(x)=sin(x2)f'(x) = -\sin(\frac{x}{2})33
  4. Simplify second derivative: Simplify the expression for the second derivative. f(x)=(12)cos(x2)f''(x) = -(\frac{1}{2})\cos(\frac{x}{2})

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