中二數學主項變換

( p + r ) a + ( p - r ) b = 0 [p]

ap + ar + bp - br = 0

ar - br = ap + bp

( a - b ) r = ( a + b ) p

( a - b ) r / ( a + b ) = p

p = ( a - b ) r / ( a + b )

以本人有限旳知識黎睇.. 5個答案中得頭同尾兩個岩架咋 發問者請小心選擇

(p+r)a+(p-r)b=0
ap + ar + bp - br = 0
p(a + b) = br - ar
p(a + b) = (br - ar) / (a + b)

2010-03-25 23:43:44 補充：
唔記得del番!

(p+r)a+(p-r)b=0
ap + ar + bp - br = 0
p(a + b) = br - ar
p = (br - ar) / (a + b)

(p+r)a+(p-r)b=0
ap+ar+bp-br=0
ar-br=ap+bp
(a-b)r=(a+b)p
(a-b)r/(a+b)=p
p=(a-b)r/(a+b)

(p+r)a+(p-r)b=0
pa+ar+bp+br=0
p(a+b)+r(a+b)=0
(a+b)(p+r)=0
p+r=1/(a+b)
p=(1/(a+b))-r

2010-03-25 23:08:23 補充：
錯左,更正返
(p+r)a+(p-r)b=0
ap+ar+bp-br=0
p(a+b)+r(a-b)=0
p(a+b)-r(a+b)=0
(p-r)(a+b)=0
p-r=0/(a+b)
p-r=0
p=r

(p+r)a+(p-r)b=0 [p]
pa+ra+pb-rb=0
pa+pb=rb-ra
p(a+b)=r(b-a)
p=r(b-a) /(a+b)
p= r (a+b) / (a-b)
p=ra+rb / a-b

Hope I can help you!

2010-03-26 16:51:06 補充：
忘了加括號

答案是r(a+b)/a-b

才對。