数学公式的推倒a+b=c,a*20+c*6=140,-c*6-b*5=-90,用三个公式算出abc的答案是多少,

Question

数学公式的推倒
a+b=c,a*20+c*6=140,-c*6-b*5=-90,用三个公式算出a b c的答案是多少,

Answer 1

a+b=c (1)
a*20+c*6=140 (2)
-c*6-b*5=-90 (3)
(1)代入(2):a*20+(a+b)*6=140
a*20+a*6+b*6=140
a*26+b*6=140 (4)
(1)代入(3):-(a+b)*6-b*5=-90
-a*6-b*6-b*5=-90
-a*6-b*11=-90
a*6+b*11=90 (5)
(4)*3:a*78+b*18=420 (6)
(5)*13:a*78+b*143=1183 (7)
(7)-(6):b*125=763
b=6.104 (8)
(8)代入(5):a*6+6.104*11=90
a*6=90-6.104*11=90-67.144=22.856
a=3.809333 (9)
(8)和(9)代入(1):c=a+b=6.104+3.809333=9.913333