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If (1 + x + 2x2) 20 = a0 + a1x + a2 x2 + a3x3 +.......+ a40x40, then a0 + a2 + a4 +........+ a38 is equal to (a) 219(220 – 1) (b) 220(219 – 1)(c) 219(220 + 1)(d) none of these |
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Answer» Correct option (a) 219(220 – 1) Explanation: Put x = 1 and x = –1 and adding we get 420+220 = 2(a0 + a2 + a4 +....+ a38 + a40) ⇒ 239 + 219 = a0 + a2 + ..... + a38 + 220 ∴ a0 + a2 + a4 +.....+ a38 =239 + 219 – 220 = 219(220 + 1– 2) = 219(220 – 1) |
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