sin2x=tanx
looks simple, yet confusing
interval [0, 360]degrees
looks simple, yet confusing
interval [0, 360]degrees
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sin(2x) = tan(x) ← Convert to sine & cosine
2sin(x)cos(x) = sin(x)/cos(x) ← used identity sin2θ = 2sinθcosθ
2sin(x)cos²(x) = sin(x) ← multiplied both sides by cos(x)
2sin(x)cos²(x) - sin(x) = 0 ← Note: I didn't divide both sides by sine because
that might loose part of the solution
sin(x)[2cos²(x) - 1] = 0
Possible solutions are for:
➊ sin(x) = 0
x = 0°, 180°, 360° ✔ ← All three work in the original equation
➋ 2cos²(x) - 1 = 0
cos²(x) = ½
cos(x) = ±√(½)
cos(x) = ±(√2)/2 ← Note: cos(45°) = (√2)/2
x = 45°, 135°, 225°, 315° ✔ ← All three work in the
original equation
ANSWER
x = 0°, 45°, 180°, 135°, 225°, 315°, 360°
——————————————————————————————————————
sin(2x) = tan(x) ← Convert to sine & cosine
2sin(x)cos(x) = sin(x)/cos(x) ← used identity sin2θ = 2sinθcosθ
2sin(x)cos²(x) = sin(x) ← multiplied both sides by cos(x)
2sin(x)cos²(x) - sin(x) = 0 ← Note: I didn't divide both sides by sine because
that might loose part of the solution
sin(x)[2cos²(x) - 1] = 0
Possible solutions are for:
➊ sin(x) = 0
x = 0°, 180°, 360° ✔ ← All three work in the original equation
➋ 2cos²(x) - 1 = 0
cos²(x) = ½
cos(x) = ±√(½)
cos(x) = ±(√2)/2 ← Note: cos(45°) = (√2)/2
x = 45°, 135°, 225°, 315° ✔ ← All three work in the
original equation
ANSWER
x = 0°, 45°, 180°, 135°, 225°, 315°, 360°
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double-angle formula
sin(2x) = 2sin(x)cos(x)
2sin(x)cos(x) = tan(x)
2sin(x)cos(x) = sin(x)/cos(x)
2cos(x) = 1/cos(x)
2cos²(x) = 1
2cos²(x) = cos²(x) + sin²(x) pythagorean identity
cos²(x) = sin²(x)
x = 45°, 135°, 225°, 315°
sin(2x) = 2sin(x)cos(x)
2sin(x)cos(x) = tan(x)
2sin(x)cos(x) = sin(x)/cos(x)
2cos(x) = 1/cos(x)
2cos²(x) = 1
2cos²(x) = cos²(x) + sin²(x) pythagorean identity
cos²(x) = sin²(x)
x = 45°, 135°, 225°, 315°
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sin 90 = 1
tan 45 = 1
x = 45 degrees
sin 270 = -1
tan 135 = -1
x = 135 degrees
[45, 135]
tan 45 = 1
x = 45 degrees
sin 270 = -1
tan 135 = -1
x = 135 degrees
[45, 135]