Rút gọn (x-10) ²-x(x+80) (2x+9) ²-x(4x+31) 4x ²-28x+49 x ³-9x ²+27x-27 21/08/2021 Bởi Remi Rút gọn (x-10) ²-x(x+80) (2x+9) ²-x(4x+31) 4x ²-28x+49 x ³-9x ²+27x-27
`(x-10)^2 – x(x+80) = x^2 – 20x + 100 – x^2 – 80x = -100x + 100` `4x^2-28x+49 = 4(x^2 – 7x + 49/4) = 4(x – 7/2)^2` `x^3-9x^2+27x – 27 = x^3 – 3.x^2 . 3 + 3.x.3^2 – 3^3 = (x-3)^3` Bình luận
Giải thích các bước giải: a) $(x-10)^2-x(x+80)$ $=x^2-20x+100-x^2-80x$ $=(x^2-x^2)-(20x+80x)+100$ $=-100x+100$ $=100(1-x)$ b) $(2x+9)^2-x(4x+31)$ $=4x^2+36x+81-4x^2-31x$ $=(4x^2-4x^2)+(36x-31x)+81$ $=5x+81$ c) $4x^2-28x+49$ $=(2x-7)^2$ d) $x^3-9x^2+27x-27$ $=(x-3)^3$ Học tốt!!! Bình luận
`(x-10)^2 – x(x+80) = x^2 – 20x + 100 – x^2 – 80x = -100x + 100`
`4x^2-28x+49 = 4(x^2 – 7x + 49/4) = 4(x – 7/2)^2`
`x^3-9x^2+27x – 27 = x^3 – 3.x^2 . 3 + 3.x.3^2 – 3^3 = (x-3)^3`
Giải thích các bước giải:
a) $(x-10)^2-x(x+80)$
$=x^2-20x+100-x^2-80x$
$=(x^2-x^2)-(20x+80x)+100$
$=-100x+100$
$=100(1-x)$
b) $(2x+9)^2-x(4x+31)$
$=4x^2+36x+81-4x^2-31x$
$=(4x^2-4x^2)+(36x-31x)+81$
$=5x+81$
c) $4x^2-28x+49$
$=(2x-7)^2$
d) $x^3-9x^2+27x-27$
$=(x-3)^3$
Học tốt!!!