数学问题111a+b+c=56b平方=ac求b我想出来了..还是谢谢各位``

Question

数学问题111
a+b+c=56 b平方=ac 求b
我想出来了..还是谢谢各位``

Answer 1

((a+c-56)^2=b^2=ac
(a+c)^2-112(a+c)+56^2=ac
(a+c)^2=a^2+c^2+2ac
(56-b)^2=(a+c)^2>=4ac=4b^2
56^2-112b+b^2>=4b^2
3b^2+112b-56^2<=0
(b+56)(3b-56)<=0
-56<=b<=56/3