Đáp án+Giải thích các bước giải:

$\color{#a8b0b4}{⸻}\color{#91999d}{⸻}\color{#7a8286}{⸸}\color{#636b6f}{⛧}
\color{#4c5356}{𝕯}\color{#434a4d}{ψ}\color{#3b4244}{ภ}\color{#32393b}{ค}
\color{#2a3133}{๓}\color{#21282a}{๏}\color{#1a2123}{ภ}\color{#141a1c}{ร}
\color{#0f1516}{ฬ}\color{#0a1011}{๏}\color{#05090a}{ɭ}\color{#020406}{๔}
\color{#05090a}{⛧}\color{#0a1011}{⸸}\color{#141a1c}{⸻}\color{#1a2123}{⸻}$

 `(x+4).(-x^{2}+6x+5)`

`=x.(-x^{2}+6x+5)+4.(-x^{2}+6x+5)`

`=-x^{3}+6x^{2}+5x-4x^{2}+24x+20`

`=-x^{3}+(6x^{2}-4x^{2})+(5x+24x)+20`

`=-x^{3}+2x^{2}+29x+20`