Pair of Straight Lines
- The acute angle between the lines represented by \(x^2-4xy+y^2=0\) is Answer: B. 60° tanθ=|2√(h²-ab)/a+b|=2√(4-1)/2=sqrt3⇒θ=60^° . 1
- If the lines represented by \(kx^2+6xy-7y^2=0\) are perpendicular, then \(k=\) Answer: A. 7 Perpendicular when a+b=0 : k-7=0⇒ k=7 . 1
- The joint equation of the lines through the origin perpendicular to the lines \(x^2-5xy+4y^2=0\) is Answer: A. 4x²+5xy+y²=0 Given lines (x-y)(x-4y)=0 have slopes 1,1/4 . Perpendicular slopes -1,-4 : (x+y)(4x+y)=0 . 1