

Range R= u2 sin2Θ/g
Maximum height H=u2 sin2 Θ /2g
According to question,
u2 sin2Θ/g =a ......(1) and
u2 sin2 Θ /2g =b .....(2)
Sin2Θ= 2sinΘ cosΘ
put this in eq (1) we get,
2u2 sinΘ cosΘ =ag
sinΘ= ag/ 2u2 cosΘ
Put this value of sinΘ in eq.(2), we get
b= a2 g /8u2 cos2 Θ
so, velocity of projection u= √a2 g /8b cos2 Θ
