find the LCM of y^2-64 and y^2+15y+56

Answer 1

Factor each to get:
y^2-64=(y-8)(y+8)
y^2+15y+56= (y+8)(y+7)

The LCM is the smallest number/expression that has all of the above factors.
In this case, there would be 3 factors, since two of the four are identical.