Do u solve this polynomial

(8a-4a^2)-(7a^3-a)

this is simply
1. distribute the negative
2. add like terms

(8a-4a^2)-(7a^3-a)=8a-4a^2+ -7a^3 +a

answer; -7a^3 - 4a^2 + 9a

You cannot solve an expression (no equal sign), you can only simplify or reduce the expression.

[8a - 4(a^2)] - [7(a^3) - a] <-- Distribute the negative and drop the parenthesis

8a - 4(a^2) - 7(a^3) + a <-- Combine like terms

ANSWER: 9a - 4(a^2) - 7(a^3)

You don't solve anything if you don't have an equation

Here