1.

ABis a vertical pole with B at the ground level and A at the top. A man findsthat the angle of elevation of the point A from a certain point C on theground is `60o`.He moves away from the pole along the line BC to a point D such that `C D""=""7""m`.From D the angle of elevation of the point A is `45o`.Then the height of the pole is(1) `(7sqrt(3))/2dot1/(sqrt(3)-1)m`(2) `(7sqrt(3))/2dot(sqrt(3)+1)m`(3) `(7sqrt(3))/2dot(sqrt(3)-1)m`(4) `(7sqrt(3))/2dot1/(sqrt(3)+1)m`

Answer» `BC=x`
`AB=y`
`tan60^@=AB/BC=y/x`
`sqrt3=y/x`
`x=y/sqrt3`
`tan45^@=(AB)/(BD)=(AB)/(DC+CB)`
`=y/(7+x)`
`=1`
`y=7+x`
`y=7+y/sqrt3`
`y-y/sqrt3=7`
`y(sqrt3-1)=7sqrt3`
`y=(7sqrt3)/(sqrt3-1)xx(sqrt3+1)/(sqrt3+1)`
`=(7sqrt3)/(3-1)xx(sqrt3+1)`
`=(7sqrt3)/(2)xx(sqrt3+1)`
option`2`


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