數學難題！暑期功課！

－3y²(2y－5)＋4y(3y²＋1)
=-6y^3-3y^2(5)+12y^3+4y(1)
=-6y^3-15y^2+12y^3+4y
=-6y^3-3y^2+4y


(3y－1)(2y²＋y－1)
=3y(2y²＋y－1)-1(2y²＋y－1)
=6y^3+3Y^2-3y-2y^2-y+1
=6y^3+Y^2-4y+1

(3x-2y)(2x+3y)
=3x(2x+3y)-2y(2x+3y)
=6x^2+9xy-4xy-6y^2
=6x^2+5xy-6y^2

(x-y) (x+2y)
=x(x+2y) - y(x+2y)
=x^2+2xy-xy-2y^2
=x^2+xy-2y^2

(2m-5) (m-4)
=2m (m-4) -5 (m-4)
=2m^2-8m-5m+20
= 2m^2-13m+20

(x+y) (x²-xy+y²)

=x(x²-xy+y²) +y(x²-xy+y²)
=x^3-(x^2)y+xy^2+(x^2)y -xy^2+ y^3
=x^3+y^3


(x-y) (x²+xy+y²)
=x (x²+xy+y²) -y (x²+xy+y²)
=x^3+ (x^2)y+ xy^2 - (x^2)y - xy^2 -y^3
=x^3- y^3

:)

- 3-
Hello~
我係小學升中一~~

聽好...
+ + = +
- - = +
+ - = -
- + = -
OK??

** 6y(2y+7㎡)
= 6y‧2y + 6y‧7㎡
= 12y² + 42㎡y ←唔順...
= 42㎡y + 12y²
OK??

我識做 , 但我唔俾你睇!!

*** (a+b)²
= (a+b)(a+b)
= a² + 2ab + b²
OK??
= = 唉~算~我俾你睇答案!
**** (2m - 5)(m - 4) 展開
= 2m‧m - 2m‧4 - 5‧m + 5 x 4
= 2m² - 8m - 5m + 20
→= 2m² - 3m + 20 ←答案
OK??

─ω─ ∕88