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Sagot :

bjr

a et b sont des angles aigus (sinus, cosinus et tangente positifs)

1)

méthode 1 :

tan a = sin a / cosa

√7/3 = sin a / (3/4)

sin a = (√7/3) x (3/4)

sin a = √7/4

méthode 2 :

sin²a + cos²a = 1

sin²a + (3/4)² = 1

sin²a = 1 - 9/16

sin²a = 16/16 - 9/16

sin²a = 7/16

sin a = √7/4

2)

cos b = 3 sin b

3 sin b = cos b

3 sin b/cos b = 1

3 tan b = 1

tan b = 1/3

sin²b + cos²b = 1

sin²b + (3sin b)² = 1

sin²b + 9 sin²b = 1

10 sin²b = 1

sin²b = 1/10

sin b = 1/√10

sin b = √10/10

cos²b = 1 - sin²b

cos²b = 1 - 1/10

cos²b = 9/10

cos b = 3/√10

cosb = 3√10/10

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