The angle of elevation of the top of a tower standing on a horizontal plane from a point `A` is `alpha` . After walking a distance d towards the foot of the tower the angle of elevation is found to be `beta` . The height of the tower is (a)`d/(cotalpha+cotbeta)` (b) `d/(cotalpha-cotbeta)` (c)`d/(tanbeta-t a nalpha)` (d) `d/(tanbeta+tanalpha)`

Explanation

`tanβ=h/x` and ` tanα=h/(d+x)`


∴`x=h/(tanβ)`


`tanα=h/(d+h/(tanβh))`
Then, `dtanα+ (htanα)/(tanβ) =h`
`h=( dtanα)/(1−tanβtanα)= (dtan.tanβ)/(tanβ−tanα)`