已知向量A=(1,2),向量b=(2,1)答:解:向量ma=(m,2m), 向量nb=(2n,n).ma+mb=(m+2n,2m+n).(a-b)=(-1.1).∵(ma+mb)⊥(a-b),∴(m+2n)*(-1)+(2m+n)*1=0.-m-2n+2m+n=0 m-n=0.m=n.m^2+n^2+2m=2m^2+2m.=2(m+1/2)^2-1/2.∵m,n∈R, (m+1/2)^2≥0.∴(m^2+n^2+2m)min=-1/...
已知向量a=(1,2),向量b=(3,4) (1)求2a,a+b,a乘b (2)若c答:(1)2a=2(1,2)=(2,4),a+b=(1+3,2+4)=(4,6)a*b=(1*3,2*4)=(3,6)(2) C=(3,m),c//a, 1*m-2*3=0,m=6.