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Ex 11.2, 11 Show that the lines (𝑥 − 5)/7 = (𝑦 + 2)/( −5) = 𝑧/1 and 𝑥/1 = 𝑦/2 = 𝑧/3 are perpendicular to each other. Two lines (𝑥 − 𝑥1)/𝑎1 = (𝑦 − 𝑦1)/𝑏1 = (𝑧 − 𝑧1)/𝑐1 and (𝑥 − 𝑥2)/𝑎2 = (𝑦 − 𝑦2)/𝑏2 = (𝑧 − 𝑧2)/𝑐2 are perpendicular to each other if 𝒂𝟏 𝒂𝟐 + 𝒃𝟏 𝒃𝟐 + 𝒄𝟏 𝒄𝟐 = 0 (𝒙 − 𝟓)/𝟕 = (𝒚 + 𝟐)/( − 𝟓) = 𝒛/𝟏 (𝑥 − 5)/7 = (𝑦 − (−2))/( −5) = (𝑧 − 0)/1 Comparing with (𝑥 − 𝑥1)/𝑎1 = (𝑦 − 𝑦1)/𝑏1 = (𝑧 − 𝑧1)/𝑐1, So, 𝑥1 = 5, y1 = −2, 𝑧1 = 0 & 𝒂𝟏 = 7, 𝒃𝟏 = − 5, 𝒄𝟏 = 1, 𝒙/𝟏 = 𝒚/𝟐 = 𝒛/𝟑 (𝑥 − 0)/1 = (𝑦 − 0)/2 = (𝑧 − 0)/3 Comparing with (𝑥 − 𝑥2)/𝑎2 = (𝑦 − 𝑦2)/𝑏2 = (𝑧 − 𝑧2)/𝑐2, So, x2 = 0, y2 = 0, z2 = 0, & 𝒂𝟐 = 1, b2 = 2, c2 = 3 So, 𝒂𝟏 𝒂𝟐 + 𝒃𝟏 𝒃𝟐 + 𝒄𝟏 𝒄𝟐 = (7 × 1) + (−5 × 2) + (1 × 3) = 7 + (−10) + 3 = 0 Therefore, the two given lines are perpendicular to each other.

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science and Computer Science at Teachoo