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### Equal sign

In mathematics, at the left and right of the equal sign (=) the same is stated.

##### Example 1

Some simple calculations are

If left and right are not identical you have a mathematical error.

##### Example 2

You can solve the equation

because for *x = *2 you get

2

^{2}= 2^{2}⇒ 4 = 4

and that's right. That you could see quickly. But there are more solutions. By careful thinking and trying you can figure them out.

##### Example 3

In Euler's formula, you can fill in the definitions of the sine and the cosine, and then you find

## HistoryThe Welsh mathematician Robert Recorde introduced the = sign in 1557 in his book |