Radio waves coming at anglealpha to veti...

Radio waves coming at `angle_alpha` to vetical are received by a radar after reflection from a nearby water surface and directly .what should be height of antenna from water surface so that it records a maximum intensity.(Wavelength =`lambda`)

`lamda/(4cosalpha)`

`(2lamda)/(4cosalpha)`

`(3lamda)/(6cosalpha)`

`(5lamda)/(7cosalpha)`

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