Question

y^2-2y^2

Answer 1

what are you trying to find?

Answer 2

so have same variable "y" and same power of variable which is "2"
so you just have to combine like terms
1 -2 = ???
remember you have 1 coefficient at front of y square

Answer 3

when you add number with variable just add number variable stay same
hope you understand
if you not feel free to ask me :) :) :)