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JEE Main 2020
Height and Distance
Height and Distance
Medium

Question

Let a vertical tower AB have its end A on the level ground. Let C be the mid-point of AB and P be a point on the ground such that AP = 2AB. If \angle BPC = β\beta , then tanβ\beta is equal to:

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Solution

Let the height of tower AB=xAB = x and LCPA=LCPA = \propto From the diagram you can see, tan(+β)=x2x=12\tan \left( { \propto + \beta } \right) = {x \over {2x}} = {1 \over 2} we know, tan(+β)=tan+tanβ1tantanβ\tan \left( { \propto + \beta } \right) = {{\tan \propto + \tan \beta } \over {1 - \tan \propto \tan \beta }} \therefore\,\,\, tan+tanβ1tantanβ=12....(1){{\tan \propto + \tan \beta } \over {1 - \tan \propto \tan \beta }} = {1 \over 2}....\left( 1 \right) From the diagram, tan^=x/22x=14......(2)\tan \widehat \propto = {{x/2} \over {2x}} = {1 \over 4}......\left( 2 \right) Putting value of tan\tan \propto in eq(1)(1), 14+tanβ114tanβ=12{{{1 \over 4} + \tan \beta } \over {1 - {1 \over 4}\tan \beta }} = {1 \over 2} 114tanβ\Rightarrow 1 - {1 \over 4}\tan \beta =12+2tanβ= {1 \over 2} + 2\tan \beta 9tanβ4=12 \Rightarrow {{9\tan \beta } \over 4} = {1 \over 2} tanβ=29 \Rightarrow \tan \beta = {2 \over 9}

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