Given the function f ( x ) = sin ( ω x + 3 π ) ( ω > 0 ) , f ( 6 π ) = f ( 3 π ) .
If f ( x ) has minimum value but no maximum value on the interval ( 6 π , 3 π ) , then find the value of ω .
If ω = b a , where a , b are positive coprime integers. submit a + b .
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The sine function is symmetric about it's minimum between two successive zeros. So ω 6 π + 3 π + ω 3 π + 3 π = 2 × 2 3 π ⟹ ω = 3 1 4
So, a = 1 4 , b = 3 and a + b = 1 7 .
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The period ω 2 π must be larger than the interval 3 π − 6 π = 6 π , otherwise the interval will include a maximum value, so ω 2 π > 6 π , which solves to ω < 1 2 .
By symmetry the minimum will be exactly between 6 π and 3 π , which is at 2 1 ( 6 π + 3 π ) = 4 π , so sin ( ω f r a c π 4 + 3 π ) = − 1 , which solves to ω = 3 1 4 for 0 < ω < 1 2 .
Therefore, a = 1 4 , b = 3 , and a + b = 1 7 .