Question

Sabendo que a + b = 13 e a^2 - b^2 = 39 determine o valor de a
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Answer 1

a + b = 13
a² - b² = 39

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a = 13 - b

a² - b² = 39

(13 - b)² - b² = 39
b² - 26b + 169 - b² = 39
-26b + 169 = 39
-26b = 39 - 169
-26b =  - 130 . (-1)
b = 130 / 26
b = 5

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a + b = 13
a + 5 = 13
a = 13 - 5
a = 8

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a² - b² = 39
8² - 5² = 39
64 - 25 = 39
39 = 39