A:a
B:b
C:﹣b
D:c
—No, I didn't. Now I still can't get one.
①周围空气的氧气 ②周围空气的CO2③周围空气的水分子④光合作用生成的葡萄糖.
已知a→=(2,-1,3),b→=(-1,4,-2),c→=(7,5,λ),若向量a→,b→,c→共面,则λ=( )