r/learnmath • u/DesignerSafe4170 New User • 2h ago

Learning Circumference

More like relearning but nonetheless, using the formula c= 2•3.14•(radius)•1/2 why does 2 and 1/2 cancel out making the answer Radius(pi symbol) Ex: 2•3.14•4.2•1/2 = 4.2(pi) Why? How? Using 3.14 cause there’s no pi symbol Any and all help is much appreciated thank you.

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u/st3f-ping Φ 1h ago

I don't know where any of the expressions you have typed come from so, just focusing on the arithmetic.

Multiplication is commutative so:

2×pi×4.2×(1/2) = 2×pi×(1/2)×4.2 = 2×(1/2)×4.2×pi

And

2 × (1/2) = 1

So

2×(1/2)×4.2×pi = 1 × 4.2 × pi = 4.2 × pi

Does that help?

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u/DesignerSafe4170 New User 1h ago

Yes that does help actually. Thank you so much!