Tan a + Tan B = - 4, Tan a, Tan B = - 7, find the value of sin ^ 2 (a + b) + 4sin (a + b) - cos ^ 2 (a + b)

Tan a + Tan B = - 4, Tan a, Tan B = - 7, find the value of sin ^ 2 (a + b) + 4sin (a + b) - cos ^ 2 (a + b)

Tan a + Tan B = - 4 and sin (a + b) = - 4cosacosb
Sin ^ 2 (a + b) + 4sin (a + b) = 0, that is - cos ^ 2 (a + b)
tan a tan b=-7,sinasinb=-7cosacosb cos (a+b)=-8cosacosb
So tan (a + b) = - 1 / 2 1 + Tan ^ 2 (a + b) = 1 / cos ^ 2 (a + b)
-cos^2 (a+b)=-4/5