Question 269066
25a^(2)-(a+5)^(2)

Squaring an expression is the same as multiplying the expression by itself 2 times.
25a^(2)-((a+5)(a+5))

Multiply -1 by each term inside the parentheses.
25a^(2)-a^(2)-10a-25

Since 25a^(2) and -a^(2) are like terms, add -a^(2) to 25a^(2) to get 24a^(2).
Answer: 24a^(2)-10a-25