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If the A.M. of two positive numbers `aa n db(a > b)`is twice their geometric mean. Prove that : `a : b=(2+sqrt(3)):(2-sqrt(3))dot`

Answer» It is given that A.M. is twice of the G.M.
`:. (a+b)/2 = 2sqrt(ab)`
`=>(a+b)/(2sqrt(ab)) = 2/1`
Using componendo and dividendo,
`=>(a+b+2sqrt(ab))/(a+b-2sqrt(ab)) = (3+1)/(3-1)`
`=>(sqrta+sqrtb)^2/(sqrta-sqrtb)^2 = 3/1`
`=>(sqrta+sqrtb)/(sqrta-sqrtb) = sqrt3/1`
Using componendo and dividendo again,
`=>(sqrta+sqrtb+sqrta-sqrtb)/(sqrta+sqrtb-sqrta+sqrtb) = (sqrt3+1)/(sqrt3-1)`
`=>(2sqrta)/(2sqrtb) = (sqrt3+1)/(sqrt3-1)`
`=> sqrta/sqrtb = (sqrt3+1)/(sqrt3-1)`
`=>a/b = (sqrt3+1)^2/(sqrt3-1)^2`
`=>a/b = (3+1+2sqrt3)/(3+1-2sqrt3)`
`=>a/b = (2+sqrt3)/(2-sqrt3)`
`:. a:b = 2+sqrt3 : 2-sqrt3`


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