# How do you factor  49-4y^2?

$\left(7 + 2 y\right) \left(7 - 2 y\right)$
Use the difference of two squares factorisation: ${a}^{2} - {b}^{2} = \left(a + b\right) \left(a - b\right)$
$49 - 4 {y}^{2} = \left(7 + 2 y\right) \left(7 - 2 y\right)$