How to find the general solution of an equation of the form sin θ = 1?
Prove that the general solution of sin θ = 1 is given by θ = (4n + 1)π/2, n ∈ Z.
Solution:
We have,
sin θ = 1
⇒ sin θ = sin \(\frac{π}{2}\)
θ = mπ + (1)\(^{m}\) ∙ \(\frac{π}{2}\), m ∈ Z, [Since, the general solution of sin θ = sin ∝ is given by θ = nπ + (1)\(^{n}\) ∝, n ∈ Z.]
Now, if m is an even integer i.e., m = 2n (where n ∈ Z) then,
θ = 2nπ + \(\frac{π}{2}\)
⇒ θ = (4n + 1)\(\frac{π}{2}\)
Again, if m is an odd integer i.e. m = 2n + 1 (where n ∈ Z) then,
θ = (2n + 1) ∙ π  \(\frac{π}{2}\)
⇒ θ = (4n + 1)\(\frac{π}{2}\).
Hence, the general solution of sin θ = 1 is θ = (4n + 1)\(\frac{π}{2}\), n ∈ Z.
1. Solve the trigonometric equation sin x  2 = cos 2x, (0 ≤ x ≤ \(\frac{π}{2}\))
Solution:
sin x  2 = cos 2x
⇒ sin x  2 = 1  2 sin 2x
⇒ 2 sin\(^{2}\) x + sin x  3 = 0
⇒ 2 sin\(^{2}\) x + 3 sin x  2 sin x  3 = 0
⇒ sin x (2 sin x + 3)  1(2 sin x + 3) = 0
⇒ (2 sin x + 3) (sin x  1) = 0
Therefore, either, 2 sin x + 3 = 0 ⇒ sin x =  \(\frac{3}{2}\), Which is impossible since the numerical value of sin x cannot be greater than 1.
or, sin x  1 = 0
⇒ sin x = 1
We know that the general solution of sin θ = 1 is θ = (4n + 1)\(\frac{π}{2}\), n ∈ Z.
Therefore, x = (4n + 1)\(\frac{π}{2}\) …………… (1) where, n ∈ Z.
Now, Putting n = 0 in (1) we get, x = \(\frac{π}{2}\)
Now, Putting n = 1 in (1) we get, x = \(\frac{5π}{2}\)
Therefore, the required solution in 0 ≤ x ≤ 2π is: x = \(\frac{π}{2}\).
11 and 12 Grade Math
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