Question

The line lx + my + n = 0 will be a tangent to the circle

x² + y² = a² iff –

• A. n² (l² + m²)= a²
• B. a² (l²+ m²) = n²
• C. n(l + m) = a
• D. a(l + m) = n

Answer 1

Answer: (B)

a² (l²+ m²) = n²

Answer 2

Centre (0, 0) ; Radius = a

line lx + my + n = 0 touches the circle

\ p = r

Ž $\left| 0 + 0 + \mathrm { n } / \sqrt { \ell ^ { 2 } + \mathrm { m } ^ { 2 } } \right|$ = a

Ž n² = a² (l² + m²)