If a - b = 6 and a2 + b2 = 116, then what is the value of ab?
20
40
60
80
Explanation:
$(a - b)^2 = a^2 - 2ab + b^2$
=> (a - b)2 = a2 - 2ab + b2
=> 62 = 116 - 2ab
=> 36 = 116 - 2ab
=> 2ab = 116 - 36 = 80
=> ab = 40
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