Find the sum, in degrees, of all θ between 0 ∘ and 3 6 0 ∘ such that
tan ( 2 θ − 3 3 0 ∘ ) = 3 .
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The question does not make clear whether the range is inclusive or exclusive, so I included the solution theta = 360, which produces 2*theta - 330 = 390, which also has the correct tangent. This gives a sum of 990, but was marked incorrect
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390 degrees does not give the right tangent. This is equivalent to 30 degrees, which gives 1/sqrt(3) as its tangent.
-300 and -120 is the value of 2 theta - 30, not theta itself...
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hey!! how can you take -300 and -240...i thought negative angle were not allowed!!! its only 60 and 240
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he said \theta must be in [0,360] whereas we see 2\theta - 330 can take values like -300,-120 which is justified
Cool. I solved the same way!
You said theta must be between 0 and 360 but you have included -300 and -120!!!!
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Well he said θ must be in [0,360] whereas we see 2 θ − 3 3 0 assumes -300,-120 which is justified.
Best of all of you other trigonometry questions!!! Keep it up!!! By the way, I also did with the same method.
using notable angles, we know that:
tan ( β ) = 3 when β = 6 0 + 1 8 0 ∗ n deg, (1) w/ n = 0 , ± 1 , ± 2 , ± 3 . . .
So, making equal the trigonometric fuction argument with (1):
⇒ 2 θ − 3 3 0 = 6 0 + 1 8 0 n
⇒ θ = 1 9 5 + 9 0 n
which values included in 0 < θ < 3 6 0 deg. are:
⇒ θ = 1 5 , 1 0 5 , 1 9 5 , 2 8 5 and suming these numbers we obtain 600 degres
according to trigonometric equations if tan(alpha)=tan(theta) then alpha=n pi+(theta), then 2x-330=n pi+60 where n is integer, solving this for n=0,1,-1,-2 we get alpha=13 pi/12, 19 pi/12, 7 pi/12, pi/12...summing this we 10 pi/3 which is 600`
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We have
0 ∘ < θ < 3 6 0 ∘
⟹ 0 ∘ < 2 θ < 7 2 0 ∘
⟹ − 3 3 0 ∘ < 2 θ − 3 3 0 ∘ < 3 9 0 ∘
Since tan is only positive when 2 θ − 3 3 0 ∘ lies in the first and third quadrant, and tan 6 0 ∘ = 3 , we have 2 θ − 3 3 0 ∘ = 6 0 ∘ , 2 4 0 ∘ .
Since tan has a periodicity of 1 8 0 ∘ , the following values of 2 θ − 3 3 0 ∘ are possible: − 3 0 0 ∘ , − 1 2 0 ∘ , 6 0 ∘ , 2 4 0 ∘ .
Thus θ = 1 5 ∘ , 1 0 5 ∘ , 1 9 5 ∘ , 2 8 5 ∘ . Summing these up we have 6 0 0 ∘ and we are done.