Q. Given that x=3y4+1, find dyd(5y2−4cosx) in terms of only y.Answer:
Apply Chain Rule: To find the derivative of the function 5y2−4cos(x) with respect to y, we need to apply the chain rule because x is a function of y. The chain rule states that the derivative of a composite function is the derivative of the outer function times the derivative of the inner function.
Find Outer Function Derivative: First, let's find the derivative of the outer function 5y2−4cos(x) with respect to x, which we will denote as f′(x). The derivative of 5y2 with respect to x is 0 since y is treated as a constant with respect to x. The derivative of −4cos(x) with respect to x is x0. So, x1.
Find Inner Function Derivative: Now, we need to find the derivative of the inner function x with respect to y, which we will denote as dydx. Given that x=3y4+1, the derivative of x with respect to y is dydx=dyd(3y4+1)=12y3.
Apply Chain Rule Again: Using the chain rule, the derivative of the function 5y2−4cos(x) with respect to y is the product of f′(x) and dydx. Therefore, dyd(5y2−4cos(x))=f′(x)⋅dydx=4sin(x)⋅12y3.
Express Derivative in Terms of y: We need to express the derivative in terms of y only. Since x=3y4+1, we can substitute this into the sine function. So, sin(x) becomes sin(3y4+1).
Write Final Expression: Now, we can write the final expression for the derivative in terms of y: dyd(5y2−4cos(x))=4sin(3y4+1)×12y3=48y3sin(3y4+1).
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