Final answer:
To find the polynomial that must be added to x²-2x+6 to get x³+7x, subtract the given polynomial from the desired polynomial. The resulting polynomial is x³-x²+9x-6.
Step-by-step explanation:
To find the polynomial that must be added to x²-2x+6 to get x³+7x, we can subtract the given polynomial from the desired polynomial. In this case, we get:
(x³+7x) - (x²-2x+6)
Simplifying, we combine like terms and rearrange the terms in descending order of exponents:
x³+7x-x²+2x-6
The resulting polynomial is x³-x²+9x-6. Therefore, x³-x²+9x-6 must be added to x²-2x+6 to have the sum of x³+7x.