the function is odd if you can replace every x with -x and get the oposite equation example if you replace x with -x in y=x^3, then you get -x^3, so therefor the functin is odd
so
replace x with -x
a. we get x^3+4, nope b. we get -2x^3, yep c. we get x^4-9, nope d. we get x^4-4x, nope
