My Math Forum Calculable tan(ϕ)

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 March 27th, 2017, 10:59 AM #1 Newbie   Joined: Mar 2017 From: Netherlands Posts: 11 Thanks: 0 Calculable tan(ϕ) Hi, Who can help me to sum below? I can not get them on. Given is the function : f(x)= -2cos(x) with Df = [0, π ] Calculate tan(ϕ) as (ϕ) the size of the angle which is where the graph of f (x) intersects the X-axis
March 27th, 2017, 11:28 AM   #2
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Quote:
 Originally Posted by westerwolde Hi, Who can help me to sum below? I can not get them on. Given is the function : f(x)= -2cos(x) with Df = [0, π ] Calculate tan(ϕ) as (ϕ) the size of the angle which is where the graph of f (x) intersects the X-axis
$f(x) = -2\cos{x} = 0$ at $x = \dfrac{\pi}{2}$ for $x \in [0,\pi]$

$\tan{\phi} = f'\left(\dfrac{\pi}{2}\right)$

March 27th, 2017, 09:43 PM   #3
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Quote:
 Originally Posted by skeeter $f(x) = -2\cos{x} = 0$ at $x = \dfrac{\pi}{2}$ for $x \in [0,\pi]$ $\tan{\phi} = f'\left(\dfrac{\pi}{2}\right)$

How do I find the angle now being asked?
According to the book should answer tan(ϕ)=2 out of here.

 March 28th, 2017, 05:24 AM #4 Math Team   Joined: Jul 2011 From: Texas Posts: 2,639 Thanks: 1318 $\phi = \arctan(2)$

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