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| − | When something is equal to something else, then they have the same value. For instance, if <math>y = 4</math>, then <math>y</math> belongs to the set of numbers {4}. You are also able to use this to prove other statements.
| + | #REDIRECT [[Equality]] |
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| − | Question: Given that <math>y = 4</math>, prove that <math>y^2 + y - 3 = 17</math>.
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| − | Solution: We can first square our original equation to get <math>y^2 = 16</math>. We can add <math>y</math> to that, as we know that <math>y</math> still equals <math>4</math>. So, <math>y^2 + y = 20</math>. We can also subtract both the left and the right side of the equation by <math>3</math>, giving us <math>y^2 + y - 3 = 17</math>. This proves what we wanted to prove.
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