use division algorithm to show that the cube of any positive integer is of the form 9m,9m+1 or 9m+8
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Let 'a' be any positive integer and b = 3
a = 3q + r, where q ≥ 0 and 0 ≤ r < 3
Case 1: When a = 3q,
Where 'm' is an integer such that m = (3q)³ = 27q³
9(3q³) = 9m
Case 2: When a = 3q + 1,
a³ = (3q +1)³
a³ = 27q³ + 27q² + 9q + 1
a³ = 9(3q³ + 3q² + q) + 1
a³ = 9m + 1
∴ Where 'm' is an integer such that m = (3q³ + 3q²+ q)
Case 3: When a = 3q + 2,
a³ = (3q +2)³
a³ = 27q³ + 54q² + 36q + 8
a³ = 9(3q³ + 6q² + 4q) + 8
a³ = 9m + 8
Where 'm' is an integer such that m = (3q³ + 6q²+ 4q)
∴The cube of any positive integer is of the form 9m, 9m + 1, or 9m + 8.
This Question is done using b = 3, if you want to do your Sum using b = 9 then, Check this Link below:
https://brainly.in/question/17313113
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