Step-by-step explanation:

1 Remove parentheses.

21{x}^{2}-17x-12{x}^{2}-1

21x

2

−17x−12x

2

−1

2 Collect like terms.

(21{x}^{2}-12{x}^{2})-17x-1

(21x

2

−12x

2

)−17x−1

3 Simplify.

9{x}^{2}-17x-1

9x

2

−17x−1