Q. Given that y=2x4+1, find dxd(y3+4cosx) in terms of only x.Answer:
Apply Chain Rule: First, we need to apply the chain rule to find the derivative of y3 with respect to x. The chain rule 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. In this case, the outer function is f(u)=u3 and the inner function is u=y, where y is a function of x.
Derivative of y3: The derivative of the outer function f(u)=u3 with respect to u is 3u2. We will substitute u with y to get 3y2.
Derivative of 4cos(x): Now we need to find the derivative of the inner function y with respect to x. Since y=2x4+1, the derivative of y with respect to x is dxdy=dxd(2x4+1)=8x3.
Combine Derivatives: Multiplying the derivative of the outer function by the derivative of the inner function, we get the derivative of y3 with respect to x: (dxd)(y3)=3y2⋅dxdy=3y2⋅8x3.
Express in Terms of x: Next, we need to find the derivative of 4cos(x) with respect to x. The derivative of cos(x) with respect to x is −sin(x), so the derivative of 4cos(x) with respect to x is −4sin(x).
Simplify Expression: Now we can combine the derivatives of y3 and 4cos(x) to find the derivative of the entire expression y3+4cos(x) with respect to x: (dxd)(y3+4cos(x))=(dxd)(y3)+(dxd)(4cos(x))=3y2⋅8x3−4sin(x).
Simplify Expression: Now we can combine the derivatives of y3 and 4cos(x) to find the derivative of the entire expression y3+4cos(x) with respect to x: (d/dx)(y3+4cos(x))=(d/dx)(y3)+(d/dx)(4cos(x))=3y2⋅8x3−4sin(x). Finally, we need to express the derivative in terms of x only. We know that y=2x4+1, so we can substitute y in the expression 3y2⋅8x3−4sin(x) with 2x4+1 to get the final derivative in terms of x: 4cos(x)1.
Simplify Expression: Now we can combine the derivatives of y3 and 4cos(x) to find the derivative of the entire expression y3+4cos(x) with respect to x: (dxd)(y3+4cos(x))=(dxd)(y3)+(dxd)(4cos(x))=3y2⋅8x3−4sin(x). Finally, we need to express the derivative in terms of x only. We know that y=2x4+1, so we can substitute y in the expression 3y2⋅8x3−4sin(x) with 2x4+1 to get the final derivative in terms of x: 4cos(x)1. Now we simplify the expression 4cos(x)2. First, we square 4cos(x)3 to get 4cos(x)4. Then we multiply this by 4cos(x)5 to get 4cos(x)6. Finally, we subtract 4cos(x)7 to get the complete expression in terms of x: 4cos(x)9.
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