Derivative of Arcsine and Arctangent?

legacyofpiracy

Junior Member
Joined
Oct 20, 2005
Messages
82
I was wondering if anyone could offer a somewhat in-depth explanation of how you would go about calculating the derivative of the arcsine/tangent/secant?

Particularily these problem..the i can just apply the method to the other ones

If F(x)=7arcsine(x^2)
F'(x)= ?


and

if F(x)=2arctan(8x^7)
F'(x)= ?


Thanks alot.
 

Unco

Senior Member
Joined
Jul 21, 2005
Messages
1,134
G'day,

If by "in-depth" you mean "to an Unco degree" and by "calculate" you mean "find"...

We have
\(\displaystyle y = 7\arcsin{x^2}\)

Divide both sides by 7:

\(\displaystyle \frac{y}{7} = \arcsin{x^2}\)

Take sin of both sides:

\(\displaystyle \sin{\frac{y}{7}} = x^2\)

Differentiate implicitly wrt x:

\(\displaystyle \frac{1}{7}\cos{\left(\frac{y}{7}\right)}\cdot \frac{dy}{dx} = 2x\)

\(\displaystyle \frac{dy}{dx} = \frac{14x}{\cos{\frac{y}{7}}\)

Now to put it terms of x only...

We had \(\displaystyle \sin{\frac{y}{7}} = x^2\) so can draw a right-angled triangle:

Code:
              /|        By Pythagoras, [sqrt(1-x^4)]^2 + (x^2)^2 = 1^2
            /  |
    1     /    |
        /      |  x^2  
      /        |
    / y/7      |      
  /____________|       y/7 is the angle, x^2 is opp
                         1 is the hyp, sqrt(1-x^4) is the adj
    sqrt(1-x^4)
And from this \(\displaystyle \cos{\left(\frac{y}{7}\right)} = \frac{adj}{hyp} = \frac{\sqrt{1-x^4}}{1} = \sqrt{1-x^4}\)

So we have
\(\displaystyle \frac{dy}{dx} = \frac{14x}{\sqrt{1-x^4}}\)

You could use trig identities just as well.
 

legacyofpiracy

Junior Member
Joined
Oct 20, 2005
Messages
82
Thanks you so much, this really helped
 
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