If two lines $a_1x + b_1y + c_1 = 0$ and $a_2x + b_2y + c_2 = 0$ are perpendicular, then:

• ক a1a2 + b1b2 = 0 ✅ সঠিক উত্তর
• খ a1/a2 = b1/b2
• গ a1b2 - a2b1 = 0
• ঘ a1a2 - b1b2 = 0