Maths! simultaneous equations (urgent)

Q1:::

p/4 - q/5=3
5p-4q=60...........(1)

q+11= 2(p-5)
q+11=2p-10
q=2p-21...........(2)

sub(2)into(1),
5p-4(2p-21)=60
5p-8p+84=60
3p=24
p=8

q=2(8)-21= -5

so p=8, q=-5
~~~~~~~~~~~~~~~~~~~~~~
Q2:::

a/2 + b/3 = 13
3a+2b=78
b=(78-3a)/2.............(1)

a/3 - b/4 =3
4a-3b=36.............(2)

sub(1)into(2),
4a-3[(78-3a)/2]=36
8a-3(78-3a)=72
8a-234+9a=72
17a=306
a=18

b=[78-3(18)]/2=12

so a=18, b=12

PS你好似唔係好熟呢類數ge計法喎
其實好簡單架咋,,從兩題裡面你可以睇到我都係用同一種方法
就係將成條式乘一個commen factor黎消滅個分母!!! [←skill!!]
eg Q2 (1)&(2)式分別乘6同埋12

當然可能有快啲ge方法,,
但用呢個方法可以好有效咁整走個好煩人ge分母
但唔好處就係一乘完之後,,啲數會變到好大
但只要你計慣左就一啲都唔難架喇~!!

p/4 - q/5=3
5p-4q=60
5p-60=4q...(1)

q+11= 2(p-5)
q+11=2p-10
q+21=2p
4q=8p-84...(2)

elim. (1) and (2),
8p-84-(5p+60)=0
3p-24=0
3p=24
p=8

sub the result into (2),
q+11=2(8-5)
q=6-11
q=-5

so p=8 and q=-5


2008-11-29 22:58:32 補充：
p/4 - q/5=3
5p-4q=60
5p-60=4q
(5p-60)/4=q...(1)

q+11= 2(p-5)
q+11=2p-10
q+21=2p...(2)

sub (1) into (2),
(5p-60)/4 +21=2p
5p-60+84=8p
24=3p
p=8