Find the derivative of px2+qx+rax+b where p,q,r,a,b are fixed non-zero constants.
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Solution
Let f(x)=px2+qx+rax+b
Differentiating with respect to x ⇒f′(x)=[(ax+b)ddx(px2+qx+r)−(px2+qx+r)ddx(ax+b)](ax+b)2 ⇒f′(x)=(2px+q)(ax+b)−a(px2+qx+r)(ax+b)2 ⇒f′(x)=2apx2+2bpx+qax+bq−apx2−qax−ar(ax+b)2 ∴f′(x)=apx2+2bpx+bq−ar(ax+b)2