about quadratic equation
问题描述：
about quadratic equation
Joan is 2 years younger than her brother Matthew,and 32 years younger than her father.Three years ago,the product of the ages of Joan and Matthew was exactly 2 times the age of their father.How old is Matthew now?PS:Ans is 13
答
J=JOAHM=MATTHEWF=FATHERM=J+2F=J+32the product of 乘积的意思因为是三年前 即 (J-3)(M-3)=2(F-3)带入前俩式子 得(J-3)(J+2-3)=2(J+32-3)解二元一次会吗然后就出来了J=11或-5(舍 因为年龄>0)M=...