当a+b分之a-b等于4时,求代数式a+b分之2乘a-b的差减去3乘a-b的差分之4乘a+b的和的值.

Question

当a+b分之a-b等于4时,求代数式a+b分之2乘a-b的差减去 3乘a-b的差分之4乘a+b的和的值.

Answer 1

a-b/a+b=4
a-b=4a+4b
3a=-5b
a=-5b/3
a+b分之2乘a-b的差减去 3乘a-b的差分之4乘a+b的和
=(2a-b)/(a+b)-(4a+b)/(3a-b)
=(2*(-5b/3)-b)/((-5b/3)+b)-(4*(-5b/3)+b)/(3*(-5b/3)-b)
=(-10b/3-b)/(-2b/3)-(-20b/3)+b)/(-15b/3-b)
=(-13b/3)/(-2b/3)-(-17b/3)/(-18b/3)
=13/2-17/18
=117-17/18
=100/18
=50/9