Question 84

If a + b = 9 and $$a^{2} + b^{2}$$ = 61, then ab is

Solution

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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