First we have to add 3x2 − 5x + 2 and − 5x2 − 8x + 9 then from the result we have to subtract 4x2 − 7x + 9.
= {(3x2 – 5x + 2) + (- 5x2 – 8x + 9)} – (4x2 – 7x + 9)
= {3x2 – 5x + 2 – 5x2 – 8x + 9} – (4x2 – 7x + 9)
= {3x2 – 5x2 – 5x – 8x + 2 + 9} – (4x2 – 7x + 9)
= {- 2x2 – 13x +11} – (4x2 – 7x + 9)
= – 2x2 – 13x + 11 – 4x2 + 7x – 9
= – 2x2 – 4x2 – 13x + 7x + 11 – 9
= – 6x2 – 6x + 2