How do you find the GCF of 21, 45?

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How do you find the GCF of 21, 45?

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Answer 1 · 2017-01-20T04:08:07

GCF of 21 and 45 is 3

Explanation:

Consider that $45 = 9 (5)$ $45=9(5)$ and $21 = 3 (7)$ $21=3(7)$

Since $3^{2} = 9$ $3^2=9$ we can say

$45 = 3^{2} (5)$ $45=3^2(5)$ Therefore 45 is divisible by 3

Since both 45 and 21 are divisible by 3 it is a common factor. Also, since 3 is the only common factor between the two numbers in their prime factorization; it is the greatest common factor of 45 and 21.

Or GCF (21,45)=3.

Another method

Since $45 = 21 (2) + 3$ $45=21(2)+3$

Then we can say

$45-=3 mod 21$

Since 3 is prime GCF (21,45)=3

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How do you find the GCF of 21, 45?

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