Q. Given the function f(x)=(8x3−9x2+9)(−9+2x2), find f′(x) in any form.Answer: f′(x)=
Product Rule Explanation: To find the derivative of the function f(x)=(8x3−9x2+9)(−9+2x2), we will use the product rule. The product rule states that the derivative of a product of two functions is the derivative of the first function times the second function plus the first function times the derivative of the second function.
Define Functions: Let's denote the first function as u(x)=8x3−9x2+9 and the second function as v(x)=−9+2x2. We need to find the derivatives u′(x) and v′(x) separately.
Derivative of u(x): First, we find the derivative of u(x)=8x3−9x2+9. Using the power rule, we get:u′(x)=dxd(8x3)−dxd(9x2)+dxd(9)u′(x)=3⋅8x3−1−2⋅9x2−1+0u′(x)=24x2−18x
Derivative of v(x): Next, we find the derivative of v(x)=−9+2x2. Again, using the power rule, we get:v′(x)=dxd(−9)+dxd(2x2)v′(x)=0+2⋅2x2−1v′(x)=4x
Apply Product Rule: Now we apply the product rule:f′(x)=u′(x)v(x)+u(x)v′(x)f′(x)=(24x2−18x)(−9+2x2)+(8x3−9x2+9)(4x)
Expand Products: We need to expand the products:f′(x)=(24x2(−9)+24x2(2x2)−18x(−9)+18x(−2x2))+(8x34x−9x24x+9⋅4x)f′(x)=(−216x2+48x4+162x−36x3)+(32x4−36x3+36x)
Combine Like Terms: Now we combine like terms:f′(x)=48x4−216x2+162x−36x3+32x4−36x3+36xf′(x)=(48x4+32x4)+(−36x3−36x3)+(−216x2)+(162x+36x)f′(x)=80x4−72x3−216x2+198x
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