Question

What should be added to 3x³-5x²+7x-4 to get 7x³+2x²-3x+9​

Answer 1

i guess this is the process if you don't understand i can explain more

Answer 2

Let the number be a.

==: a + (5x³-2x²+3x+7) = (7x³+7x-5)

==: a = (7x³+7x-5) - (5x³-2x²+3x+7)

==: a = 7x³ + 7x - 5 - 5x³+ 2x² - 3x - 7

==: a = 2x³ + 2x² + 4x - 12