中四數學題

let x and y be the two number.

x + y =27............(1)
x * y =180..........(2)

by (1)
x=27 - y ........(3)

put(3)to(2)
(27 - y)y=180
27y - y^2=180
y^2 - 27y + 180=0
(y - 12)(y - 15)=0
y=12 or y=15

for y=12
x + 12 =27
x=15

for y=15
x + 15 =27
x=12

so the two unmber is 12 and 15


希望你明啦...唔明再問我啦...~

點解要做到咁複雜, 用quadratic equation咪得囉..
let x be one no. , 27-x be the other no.
x(27-x) = 180
27x-x^2 -180 = 0
x^2 - 27x +180+0
x=15 or 12
sub x= 15 into 27-x ,, = 12
sub x= 12 into 27x,, = 15
so the two numbers are 12 and 15

Let the two number be A and B
A+B=27 AB=180--------(2)
A=27-B-----------(1)
Sub(1)into(2), it gives
(27-B)B=180
27B-B^2-180=0
B^2-27B+180=0
(B-15)(B-12)=0
B=12 OR B=15
if B=12, A=27-12=15
if B=15, A=27-15=12

Therefore, the two numbers are 12 and 15

令二數為X,Y
X+Y=27, 第一式
XY=180 第二式 ........二式解聠立
Y=27-X 代入第二式...得 X(27-X)=180......X^2-27X+180=0
(X-15)(X-12)=0................X=15 OR 12
得X=15時 Y=12 ;X=12時 Y=15...............
補充 :如何解二維方程:
1.用TRY的 二數乘積可得180 加減可得-27
2.另一個方法 代公式 aX^2+bX+c=0 X={ -b(加減)[(b^2-4ac)開根號]}/2