Step 1 :Given the expression -7a^{2} + 10a^{2}
Step 2 :Both terms are multiples of a^{2}, so they can be combined
Step 3 :The operation to be performed is addition, but one of the terms is negative
Step 4 :So, we will subtract the coefficients of the terms
Step 5 :The result of adding the coefficients is 3
Step 6 :This means that the simplified expression is 3a^{2}
Step 7 :Final Answer: \(\boxed{3a^{2}}\)