Toán (X+5)mũ ba-x mũ ba-125 Rút gọn theo hằng thức đáng nhớ{50đ} 09/07/2021 By Madeline (X+5)mũ ba-x mũ ba-125 Rút gọn theo hằng thức đáng nhớ{50đ}
(x + 5)³ – x³ – 125 = [(x + 5)³ – x³] – 125 = (x + 5 – x)[(x + 5)² + x(x + 5) + x²] – 125 = 5.(x² + 10x + 25 + x² + 5x + x²) – 125 = 5.(3x² + 15x + 25) – 125 = 15x² + 75x + 125 – 125 = (15x² + 75x) + (125 – 125) = 15x(x + 5) + 0 = 15x(x + 5) Vậy (x + 5)³ – x³ – 125 = 15x(x + 5) Trả lời
`(x+5)^3 – x^3-125`
`=x^3+15x^2+75x+125-x^3-125`
`=15x^2+75x`
`=15x(x+5)`
(x + 5)³ – x³ – 125
= [(x + 5)³ – x³] – 125
= (x + 5 – x)[(x + 5)² + x(x + 5) + x²] – 125
= 5.(x² + 10x + 25 + x² + 5x + x²) – 125
= 5.(3x² + 15x + 25) – 125
= 15x² + 75x + 125 – 125
= (15x² + 75x) + (125 – 125)
= 15x(x + 5) + 0
= 15x(x + 5)
Vậy (x + 5)³ – x³ – 125 = 15x(x + 5)