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Ex 8.1, 1 - Expand (1 - 2x)5 - Chapter 8 Class 11 Binomial

Ex 8.1,1 - Chapter 8 Class 11 Binomial Theorem - Part 2
Ex 8.1,1 - Chapter 8 Class 11 Binomial Theorem - Part 3

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Ex 8.1, 1 Expand the expression (1 – 2x)5 (1 – 2x)5 We know that (a + b)n = nC0 an + nC1 an – 1 b1 + nC2 an – 2 b2 + ….…. + nCn – 1 a1 bn – 1 + nCn bn Hence (a + b)5 = = 5!/0!( 5 − 0)! a5 + 5!/1!( 5 − 1)! a4 b1 + 5!/2!( 5 − 2)! a3 b2 + 5!/3!( 5 − 3)! a2b3 + 5!/4!( 5 − 4)! a b4 + 5!/5!( 5 −5)! b5 = 5!/(0! × 5!) a5 + 5!/(1! × 4!) a4 b + 5!/(2! 3!) a3 b2 + 5!/(3! 2!) a2b3 + 5!/(4! 1!) a b4 + 5!/(5! 0!) b5 = 5!/5! a5 + (5 × 4!)/4! a4 b + (5 × 4 × 3!)/(2! 3!) a3 b2 + (5 × 4 × 3!)/(2 × 1 ×3!) a3b2 + (5 × 4 × 3!)/(3! ×1 ×3!) a2b3 + (5 × 4!)/4! ab4 + 5!/(5! ) b5 = a5 + 5a4b + 10a3b2 + 10a2b3 + 5ab4 + b5 Thus, (a + b)5 = a5 + 5a4b + 10a3b2 + 10a2b3 + 5ab4 + b5 Putting a = 1 & b = (– 2x) (1 – 2x)5 = (1)5 + 5(1)4 (–2x) + 10 (1)3 (–2x)3 + 10 (1)2 (–2x)3 + 5 (1) (–2x)4 + (–2x)5 = 1 – 10x + 10(4x2) + 10 (–8x3) + 5 (16x4) + (–32x5) = 1 – 10x + 40x2 – 80x3 + 80x4 – 32x5

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.