Factor the expression over the complex numbers.
I believe this is how you do it.
Use the formula to factor: a^2+b^2=(a+b)(a-b)
y^2 is already a perfect square.
49=7*7=7^2 and that's your other perfect square.
Now your expression is y^2+7^2=(y-7)(y+7)
That's not quite right RP! The general expression is a2 - b2 = (a + b)(a - b)
Here we have a = y, but b = 7i, where i is the square root of -1.
So y2 + 49 → y2 - (7i)2 → (y + 7i)(y - 7i) (Note that i2 = -1)