Question

Which proportion correctly expresses the relationship between direction ratios \[(a,b,c)\] and direction cosines \[(l,m,n)\]?

Options

• \[a:b:c=\frac{1}{l}:\frac{1}{m}:\frac{1}{n}\]

• \[a^2:b^2:c^2=l:m:n\]

• \[a:b:c=l:m:n\]

• \[a+b+c=l+m+n\]

Answer 1

The triples \[(a,b,c)\] and \[(l,m,n)\] are proportional for the same line. Therefore their component ratios are equal: \[a:b:c=l:m:n\].