If a - b = 3 and $a^2$+ $b^2$= 29, then find the value of ab



[ A ]    10
right
[ B ]    12
[ C ]    15
[ D ]    18
Answer : Option A
Explanation :
$A^2$+$b^2$=29….(i)

And a-b =3….(ii)

Now ,squaring both sides of the equation (ii),We have,

$(a-b)^2$=$(3)^2$

=$a^2$+$b^2$-2ab=9

=29-2ab=9 [So,$a^2$+$b^2$=29(given)]

=-2ab=-20

= ab = $20\over 2$ = 10

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