Considering ∣∣¯¯¯a∣∣=14, ∣∣¯¯b∣∣=18, So, ∣∣¯¯¯a−¯¯b∣∣=16 and Q=¯¯¯a∧¯¯b
So, ∣∣¯¯¯a−¯¯b∣∣=16=√∣∣¯¯¯a∣∣2+∣∣¯¯b∣∣2−2∣∣¯¯¯a∣∣∣∣¯¯b∣∣cosθ
256=196+324−2(14)(18)cosθ
So cosθ=0.523
other diagonal will be
∣∣¯¯¯a+¯¯b∣∣=√∣∣¯¯¯a∣∣2+∣∣¯¯b∣∣2+2∣∣¯¯¯a∣∣∣∣¯¯b∣∣cosθ
∣∣¯¯¯a+¯¯b∣∣=√142+182+2(14)(18)(0.523)
So, ∣∣¯¯¯a+¯¯b∣∣= other diagonal =27.99≈28cm