Find the missing term.

The sum of 2ab2 and (-5ab2) is the same as the sum of (-6ab2)

2ab^2 + (-5ab^2) = 2ab^2 - 5ab^2 = - 3ab^2

the ab^2's stay the same ... ur just messing with the coefficients.

so - 3 + what is - 6? - 3 + (-3) = - 6

therefore, - 6ab^2 + (-3ab^2) = - 6ab^2 - 3ab^2 = - 3ab^2

so ur answer is : - 3ab^2