Vector ,which is directed along an x axis,is to be added to vector ,which has a magnitude of 7.4 m.The sum is a third vector that is directed along the y axis,with a magnitude that is 4.3 times that of .What is the magnitude of 帮个忙~..如果解

Vector ,which is directed along an x axis,is to be added to vector ,which has a magnitude of 7.4 m.The sum is a third vector that is directed along the y axis,with a magnitude that is 4.3 times that of .What is the magnitude of 帮个忙~..如果解
Vector ,which is directed along an x axis,is to be added to vector ,which has a magnitude of 7.4 m.The sum is a third vector that is directed along the y axis,with a magnitude that is 4.3 times that of .What is the magnitude of
帮个忙~..如果解不出给个翻译也好

Vector ,which is directed along an x axis,is to be added to vector ,which has a magnitude of 7.4 m.The sum is a third vector that is directed along the y axis,with a magnitude that is 4.3 times that of .What is the magnitude of 帮个忙~..如果解
一个向量,方向是沿x轴,这个向量与另一个长度为7.4m的向量相加,得到第三个向量,第三个向量是沿y轴,且长度为第一个向量的4.3倍,求第一个向量的长度.
设所求向量长度为x,则第三个向量长度为4.3x,由勾股定理得
x^2+(4.3 x)^2=7.4 ^2
解得x=1.676m