已知x-2的算术平方根是2,2x+y+7的立方根是3,求x2+y2的平方根。
解: x-2=4,
2x+y+7=27
x=6,y=8
x2+y2的平方根是±10。
检查视力时,眼睛与视力表应相距5米。如图所示,如果视力表离平面镜3米,人离平面镜的距离应是________米。
It has been proved _____ eating vegetables in childhood helps to protect you against serious illnesses
in later life. [ ]
A. if
B. because
C. when
D. that