Question

what should be added to 7x²+8x+10 to get 15x-x²-4?

Answer 1

Let y should be added,

7x²+8x+10+y =15x-x²-4

y=(15x-x²-4)-(7x²+8x+10)

y=15x-x²-4-7x²-8x-10

y=15x-8x-x²-7x²-10-4

y=7x-8x²-14.
.

Then,

7x-8x²-14 should be added