If a + b = 9 and $$a^{2} + b^{2}$$ = 61, then ab is
Given : $$(a + b) = 9$$ and $$a^2 + b^2 = 61$$
Using $$(a + b)^2 = a^2 + b^2 + 2ab$$
=> $$(9)^2 = 61 + (2 \times ab)$$
=> $$2 ab = 81 - 61 = 20$$
=> $$ab = \frac{20}{2} = 10$$
=> Ans - (B)
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