x/4+2(86-x)/7=23解：两边都乘以28，得7x+8(86-x)=644去括号，得7x+688-8x=644移项，得7x-8x=644-688合并同类项，得-x=-44两边都除以-1，得x=44
看
x2-28x+197 Δ=b2-4ac =282-4X1X197 =784-788 =-4<0 Δ<0，该方程在实数域内无解.
