Find Inverse Cotangent Derivative: We need to find the derivative of the inverse cotangent function, which is cot−1(8x+91). Let's denote u=8x+91. The derivative of cot−1(u) with respect to u is −1+u21. We will use the chain rule to find the derivative with respect to x.
Derivative of u: First, find the derivative of u=8x+91 with respect to x. The derivative of 8x+91 is −(8x+9)28, using the power rule and the chain rule.
Apply Chain Rule: Now, apply the chain rule. The derivative of cot−1(u) with respect to x is the derivative of cot−1(u) with respect to u multiplied by the derivative of u with respect to x. This gives us −1+u21⋅(−(8x+9)28).
Substitute u: Substitute u back into the expression to get the derivative with respect to x. The derivative of cot−1(8x+91) with respect to x is −1+(8x+91)21⋅(−(8x+9)28).
Simplify Expression: Simplify the expression. The denominator of the first fraction becomes 1+(8x+91)2=(8x+9)2(8x+9)2+(8x+9)21=(8x+9)2((8x+9)2+1). The derivative simplifies to −((8x+9)2(8x+9)2+1)1×(−(8x+9)28).
Combine Fractions: Combine the fractions by multiplying the numerators and denominators. This gives us (−1×−8)/(((8x+9)2+1)/(8x+9)2×(8x+9)2) which simplifies to 8/((8x+9)2+1).