Question

已知根号（7x+9x+13)+根号（7x-5x+13)=7x,求x

Answer 1

令m=√(7x^2+9x+13),n=√(7x^2-5x+13) 则m+n=7x m^2-n^2=(m+n)(m-n)=14x 所以m-n=2 所以m=(7x+2)/2=√(7x^2+9x+13) 平方即可简单求解21x^2-8x-48=0,(3x+4)(7x-12)=0,x=-4/3(不符题意舍去）,x=12/7 祝你学业进步!