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Mathematics

If (p + q)-1(p-1 + q-1) = paqb, prove that a + b +2 = 0, where p and q are different positive primes.

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Answer

Given,

(p+q)1(p1+q1)=paqb1(p+q)(1p+1q)=paqb1(p+q)×p+qpq=paqb1pq=paqbp1q1=paqba=1 and b=1.\Rightarrow (p + q)^{-1}(p^{-1} + q^{-1}) = p^aq^b \\[1em] \Rightarrow \dfrac{1}{(p + q)}\Big(\dfrac{1}{p} + \dfrac{1}{q}\Big) = p^aq^b \\[1em] \Rightarrow \dfrac{1}{(p + q)} \times \dfrac{p + q}{pq} = p^aq^b \\[1em] \Rightarrow \dfrac{1}{pq} = p^aq^b \\[1em] \Rightarrow p^{-1}q^{-1} = p^aq^b \\[1em] \therefore a = -1 \text{ and } b = -1.

Substituting values of a and b in L.H.S. of a + b + 2 = 0 we get,

a + b + 2 = -1 + (-1) + 2 = -2 + 2 = 0.

Hence, proved that a + b + 2 = 0.

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