Question

Evaluate the following using suitable identities: (i) (99)3 (ii) (102)3 (iii) (998)3

Answer 1

It is known that,

(a + b)3 = a3 + b3 + 3ab(a + b)

nd (a - b)3 = a3 - b3 - 3ab (a - b)

(i) (99)3 = (100 − 1)3

= (100)3 − (1)3 − 3(100) (1) (100 − 1)

= 1000000 − 1 − 300(99)

= 1000000 − 1 − 29700

= 970299

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(ii) (102)3 = (100 + 2)3

= (100)3 + (2)3 + 3(100) (2) (100 + 2)

= 1000000 + 8 + 600 (102)

= 1000000 + 8 + 61200

= 1061208

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(iii) (998)3= (1000 − 2)3

= (1000)3 − (2)3 − 3(1000) (2) (1000 − 2)

= 1000000000 − 8 − 6000(998)

= 1000000000 − 8 − 5988000

= 1000000000 − 5988008

= 994011992.