If A ≥0,B≥0,A+B=π3 and y=tanAtanB then
y=tanA.tan(π3−A)
⇒ tan2A+√3(y−1)tanA+y=0
As tan A is real , D ≥0⇒3(y−1)2−4y≥0
∴ 3y2−10y+3≥0⇒y≤13 or y≥3