First slide

Binomial theorem for positive integral Index

Question

$The unit digit of 17^{2009} + 11^{2009} - 7^{2009} is$

Moderate

A

1
B

2
C

7
D

9

Solution

$\begin{array}{l} 17^{2009} + 11^{2009} - 7^{2009} = (10 + 7)^{2009} + (10 + 1)^{2009} + - 7^{2009} \\ ∴ Unit digit = 1 \end{array}$

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