Question

evaluate 209² using suitable identities ​

Answer 1

Answer:

$209 {}^{2} \\ \\= (200 + 9) {}^{2} \\ \\= (200) {}^{2} + (9) {}^{2} + 2 \times 200 \times 9 \\ \\= 40000 + 81 + 3600 \\ \\= 43681$

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★ Identity Used -

( a + b )² = a² + b² + 2ab

Answer 2

209²= (210-1)²

= 210²-420+1 ....(a-b)²=a²-2ab+b²

= 44100-420+1

= 43681.