Find dy/dx if y=(ln(x))(cos(x))y = (ln(x))^(cos(x)).

Answer: dydx=(ln⁡x)cos⁡x(−sin⁡x⋅ln⁡(ln⁡x)+cos⁡xxln⁡x)\frac{dy}{dx} = (\ln x)^{\cos x} \left( -\sin x \cdot \ln(\ln x) + \frac{\cos x}{x \ln x} \right)

Step-by-step solution

Step 1: Take logarithm on both sides

To differentiate a function of the form f(x)^{g(x)}, we use logarithmic differentiation. We start by taking the natural logarithm on both sides of the equation.

Step 2: Apply logarithm property

Using the logarithm property ln⁡(ab)=bln⁡a\ln(a^b) = b \ln a we can simplify the right-hand side of the equation.

Step 3: Differentiate both sides with respect to x

Now, we differentiate both sides of the equation with respect to x. On the left side, we use the chain rule. On the right side, we will use the product rule.

Step 4: Apply product rule and chain rule

Applying the product rule ddx(uv)=u′v+uv′\frac{d}{dx}(uv) = u'v + uv' to the right side, where u=cos⁡xu = \cos x and v=ln⁡(ln⁡x)v = \ln(\ln x). We also use the chain rule for differentiating ln⁡(ln⁡x)\ln(\ln x).

Step 5: Isolate dy/dx

To find dydx\frac{dy}{dx}, we multiply both sides of the equation by y.

Step 6: Substitute y back into the equation

Finally, we substitute the original expression for y, which is (ln⁡x\ln x)^{cos⁡x\cos x}, back into the equation to get the derivative in terms of x only.

More from this chapter

All Continuity and Differentiability solutions →

Solve your own maths question free →