Find each sum.
(–4c2 + 7cd + 8d) + (–3d + 8c2 + 4cd) =

To add monomials, you have to look at the variables that are accompanied by their coefficients. In the given problem, (–4c2 + 7cd + 8d) + (–3d + 8c2 + 4cd), you can combine both cd ut nt cd and c² and cd and d and d and c² because they have different variables.

(–4c2 + 7cd + 8d) + (–3d + 8c2 + 4cd) 
(-4c² + 8c²) + (7cd + 4cd) + (8d - 3d)
4c² + 11cd + 5d

Acute triangles are angles below 90 degrees
Right angles are 90 degrees if that's what your asking