Q. - Let f be a function such that f(9)=−54 and f′(9)=6.- Let h be the function h(x)=x.Evaluate dxd[h(x)f(x)] at x=9.
Quotient Rule Derivative: To find the derivative of the function h(x)f(x) at x=9, we will use the quotient rule for derivatives. The quotient rule states that if we have a function g(x)=v(x)u(x), then its derivative g′(x) is given by g′(x)=(v(x))2u′(x)v(x)−u(x)v′(x). Here, u(x)=f(x) and v(x)=h(x)=x.
Derivative of f(x): First, we need to find the derivative of u(x)=f(x). We are given that f′(9)=6, which means that the derivative of f(x) at x=9 is 6.
Derivative of sqrt(x): Next, we need to find the derivative of v(x)=h(x)=x. The derivative of x with respect to x is (1/2)x(−1/2). So, v′(x)=(1/2)x(−1/2).
Evaluate v′(x) at x=9: Now we will evaluate v′(x) at x=9. Substituting x with 9, we get v′(9)=(1/2)9(−1/2)=(1/2)(1/9)=(1/2)(1/3)=1/6.
Values of u(9) and v(9): We also need the values of u(9) and v(9) to use in the quotient rule formula. We are given that f(9)=−54, so u(9)=−54. We also have v(9)=h(9)=9=3.
Apply Quotient Rule: Now we can apply the quotient rule. We have all the necessary values:u′(9)=6,v(9)=3,u(9)=−54,v′(9)=61.Substituting these into the quotient rule formula, we get:g′(9)=(v(9))2u′(9)v(9)−u(9)v′(9)g′(9)=(3)26×3−(−54)×(61)
Simplify the Expression: Simplify the expression:g′(9)=918+9g′(9)=927g′(9)=3
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