Question

Which expression is not a perfect square trinomial?
169-26y+y^2
81+18y+y^2
64+8y+y^2
25+10y+y^2

Answer 1

The answer is 64+8y+y².

In a perfect square trinomial, you can divide the value of b by 2 and square it, and it will equal the value of c.  This works in every other trinomial listed except this one:

8/2 = 4; 4²=16≠64.