Đáp án:
Giải thích các bước giải:
bài 3:
$a)112.(112-24)+144$
$=112.88+144$
$=(100+12).(100-12)+12^2$
$=100^2-12^2+12^2$
$=10000$
$b)167^2+23^2-46.167-24^2$
$=(167^2-2.23.167+23^2)-24^2$
$=(167-23)^2-24^2$
$=144^2-24^2$
$=(144-24).(144+24)$
$=120.166$
$=19920$
bài 4:
$a)(x+4).(x^2-4x+16)-x.(x-3).(x+3)=12$
$⇔x^3+64-x.(x^2-9)-12=0$
$⇔x^3-x^3+9x+52=0$
$⇔9x=-52$
$⇔x=-\dfrac{52}{9}$
$b)x^3-3x^2+3x-1+8=0$
$⇔(x-1)^3=8$
$⇔x-1=2$
$⇔x=3$
$c)(x+6).(x^2-6x+36)-x.(x-2).(x+2)=12$
$⇔x^3+216-x.(x^2-8)-12=0$
$⇔x^3-x^3+8x+204=0$
$⇔8x=-204$
$⇔x=-\dfrac{51}{2}$
$d)x^3+3x^2+3x-26=0$
$⇔x^3+3x^2+3x+1-27=0$
$⇔(x+1)^3=27$
$⇔(x+1)^3=3^3
$⇔x+1=3$
$⇔x=2$
