Question 1

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Jambmaths question: 

If $y={{(1-2x)}^{3}}$Find the value of $\frac{dy}{dx}$at x =1

Option A: 

– 6

Option B: 

57

Option C: 

–54

Option D: 

27

Jamb Maths Solution: 

$\begin{align}  & y={{(1-2x)}^{3}} \\ & \text{Using the generalised power rule method} \\ & y={{[f(x)]}^{n}} \\ & \frac{dy}{dx}=n{{[f(x)]}^{n-1}}\cdot {{f}^{1}}(x) \\ & y={{(1-2x)}^{3}} \\ & \frac{dy}{dx}=3{{(1-2x)}^{3-1}}\centerdot \frac{d}{dx}(1-2x)=3{{(1-2x)}^{2}}(-2) \\ & \frac{dy}{dx}=-6{{(1-2x)}^{2}} \\ & \text{At }x=-1 \\ & \frac{dy}{dx}\left| _{x=1} \right.=-6{{[1-2(-1)]}^{2}}=-6{{\left[ 1+2 \right]}^{2}}=-54 \\\end{align}$

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