Q.

Two numbers x and y have arithmetic mean 9 and geometric mean 4. Then x and y are the roots of

1 x2-18x-16=0  
2 x2-18x+16=0  
3 x2+18x-16=0  
4 x2+18x+16=0  

Ans.

(2)

Given, arithmetic mean of x and y is 9.

i.e.,  x+y2=9  ⇒  x+y=18

Geometric mean of x and y is 4, i.e., xy=4  ⇒  xy=16

Now, sum of roots (x+y)=18

Product of roots (xy)=16

∴ Required quadratic equation is x2-18x+16=0