(B) If the problems of a straight line are m, n, then prove that 12 + m + n = 1

If the direction cosines of a straight line are l,m and n, then prove that l^(2)+m^(2)+n^(2)=1

If l,m and n are three straight lines such that l||m and l||n then prove that m||n .

If l_(1), m_(1), n_(1) and l_(2), m_(2), n_(2) are direction cosines of two mutually perpendicular straight lines, then prove that the direction cosines of the straight line which is perpendicular to both the given lines are pm (m_(1)n_(2)-m_(2)n_(1)), pm (n_(1)l_(2)-n_(2)l_(1)), pm (l_(1)m_(2)-l_(2)m_(1))

In the adjoining figure, POQ is a straight line. Find the m and n when m:n=7:5

If straight line lx + my + n=0 is a tangent of the ellipse x^2/a^2+y^2/b^2 = 1, then prove that a^2 l^2+ b^2 m^2 = n^2.

If straight line lx + my + n=0 is a tangent of the ellipse x^2/a^2+y^2/b^2 = 1, then prove that a^2 l^2+ b^2 m^2 = n^2.

If straight line lx + my + n=0 is a tangent of the ellipse x^2/a^2+y^2/b^2 = 1, then prove that a^2 l^2+ b^2 m^2 = n^2.

Let l_(1), m_(1), n_(1) and l_(2), m_(2), n_(2) be the direction ratios of two given straight lines. Find the direction ratios of a straight line which is perpendicular to both the given straight lines.

In the adjoining figure, POQ is a straight line. Find the m and n when (i) m-n=60^(@) (ii) m:n=7.5

If m and n are positive integers, then prove that the coefficients of x^(m) " and " x^(n) are equal in the expansion of (1+x)^(m+n)