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Find the derivative of tan1(18x+9) \tan^{-1}\left(\frac{1}{8x+9}\right) .

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Q. Find the derivative of tan1(18x+9) \tan^{-1}\left(\frac{1}{8x+9}\right) .
  1. Identify Functions: We need to find the derivative of the function y=tan1(18x+9) y = \tan^{-1}\left(\frac{1}{8x+9}\right) . To do this, we will use the chain rule, which states that the derivative of a composite function is the derivative of the outer function evaluated at the inner function times the derivative of the inner function.
  2. Derivative of Outer Function: First, let's identify the outer function and the inner function. The outer function is tan1(u) \tan^{-1}(u) , where u u is the inner function. The inner function is 18x+9 \frac{1}{8x+9} .
  3. Derivative of Inner Function: The derivative of the outer function tan1(u) \tan^{-1}(u) with respect to u u is 11+u2 \frac{1}{1+u^2} . We will apply this after we find the derivative of the inner function.
  4. Apply Chain Rule: The derivative of the inner function 18x+9 \frac{1}{8x+9} with respect to x x is found using the quotient rule or recognizing it as (8x+9)1 (8x+9)^{-1} and using the power rule. The derivative is 8(8x+9)2 -\frac{8}{(8x+9)^2} .
  5. Simplify Expression: Now we apply the chain rule. The derivative of y y with respect to x x is the derivative of the outer function evaluated at the inner function times the derivative of the inner function. This gives us:\newlineddx[tan1(18x+9)]=11+(18x+9)2(8(8x+9)2) \frac{d}{dx} \left[ \tan^{-1}\left(\frac{1}{8x+9}\right) \right] = \frac{1}{1+\left(\frac{1}{8x+9}\right)^2} \cdot \left( -\frac{8}{(8x+9)^2} \right) .
  6. Final Derivative: Simplify the expression. The (8x+9)2 (8x+9)^2 in the denominator of the derivative of the inner function cancels with the (8x+9)2 (8x+9)^2 in the 1+(18x+9)2 1+\left(\frac{1}{8x+9}\right)^2 term, leaving us with:\newlineddx[tan1(18x+9)]=81+(8x+9)2 \frac{d}{dx} \left[ \tan^{-1}\left(\frac{1}{8x+9}\right) \right] = -\frac{8}{1+(8x+9)^2} .
  7. Final Derivative: Simplify the expression. The (8x+9)2 (8x+9)^2 in the denominator of the derivative of the inner function cancels with the (8x+9)2 (8x+9)^2 in the 1+(18x+9)2 1+\left(\frac{1}{8x+9}\right)^2 term, leaving us with:\newlineddx[tan1(18x+9)]=81+(8x+9)2 \frac{d}{dx} \left[ \tan^{-1}\left(\frac{1}{8x+9}\right) \right] = -\frac{8}{1+(8x+9)^2} .The final simplified form of the derivative is:\newlineddx[tan1(18x+9)]=81+64x2+144x+81 \frac{d}{dx} \left[ \tan^{-1}\left(\frac{1}{8x+9}\right) \right] = -\frac{8}{1+64x^2+144x+81} .

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