For this case we must simplify the following expression:
![(-3x ^ 2-9x + 17) - (15x ^ 2 + 20x-4) =](https://img.qammunity.org/2020/formulas/mathematics/college/hk9xusfh4ra0wjtqcqzi0o0o7pv09xcdn2.png)
We must bear in mind that by law of signs of multiplication it is fulfilled that:
![- * + = -\\- * - = +](https://img.qammunity.org/2020/formulas/mathematics/middle-school/l6tybxzhxxtn4zkcl4idfs0mtmuph9tww1.png)
Then, rewriting:
![-3x ^ 2-9x + 17-15x ^ 2-20x + 4 =](https://img.qammunity.org/2020/formulas/mathematics/college/f3ugt970uw7jkx1gucg0fadfu7ozepm2ef.png)
We add similar terms:
![-3x ^ 2-15x ^ 2-9x-20x + 17 + 4 =](https://img.qammunity.org/2020/formulas/mathematics/college/3wolcnsbvo8vh5yagl768vd9drsu7nwdi4.png)
We have that equal signs are added and the same sign is placed, while different signs are subtracted and the sign of the major is placed, then:
![-18x ^ 2-29x + 21](https://img.qammunity.org/2020/formulas/mathematics/college/vrl5t483r4layao61kaqoz6egwek0cgh2s.png)
Answer:
![-18x ^ 2-29x + 21](https://img.qammunity.org/2020/formulas/mathematics/college/vrl5t483r4layao61kaqoz6egwek0cgh2s.png)