Engineering
Mathematics
Successive Differentiation
Question

Let f(x) = (x32x2+x)(πx1)+(1+x2+x4)(1x+x2) and g(x) = sin2 x. If r=01d2gdx2|x=f'(r) = a (cos α) (cos β), where a, α, β  N, then the find value of (a + α + β) /2

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Solution

f (x) = x(πx1)(x1)21x+x2ϕ(x)  +  1+x+x2
f ' (x) = ϕ ' (x) + 1 + 2x        {ϕ ' (0) = ϕ ' (1) = 0}
f ' (0) = 1,  f ' (1) = 3
g (x) = sin2x    ⇒    g ' (x) = sin 2x    ⇒    g '' (x) = 2 cos 2x
Now,    g '' (x) |x = f ' 0) + g '' (x) |x = f ' (1) = g '' (1) + g '' (3)
                        = 2 cos 2 + 2 cos 6 = 2 (2 cos 4 · cos 2)
                        = 4 cos 2 cos 4  a cos α cos β
   a + α + β = 4 + 2 + 4 / 2 = 5