Math Problem Statement

3sin(wt) - 2cos(wt) convert to phasor form

Solution

To convert 3sin(ωt)2cos(ωt)3\sin(\omega t) - 2\cos(\omega t) into phasor form, we combine the sinusoidal terms into a single expression of the form:

Asin(ωt+ϕ)A \sin(\omega t + \phi)

Steps:

  1. Express sin(ωt)\sin(\omega t) and cos(ωt)\cos(\omega t) in terms of sin(ωt+ϕ)\sin(\omega t + \phi):

    • Recall the trigonometric identity: sin(ωt+ϕ)=sin(ωt)cos(ϕ)+cos(ωt)sin(ϕ)\sin(\omega t + \phi) = \sin(\omega t)\cos(\phi) + \cos(\omega t)\sin(\phi)

    We need to rewrite 3sin(ωt)2cos(ωt)3\sin(\omega t) - 2\cos(\omega t) in this form.

  2. Find the magnitude AA:

    • Let A=a2+b2A = \sqrt{a^2 + b^2}, where a=3a = 3 and b=2b = -2. A=32+(2)2=9+4=13A = \sqrt{3^2 + (-2)^2} = \sqrt{9 + 4} = \sqrt{13}
  3. Find the phase angle ϕ\phi:

    • ϕ=arctan(ba)=arctan(23)\phi = \arctan\left(\frac{b}{a}\right) = \arctan\left(\frac{-2}{3}\right).
    • ϕ33.69\phi \approx -33.69^\circ (in degrees) or ϕ0.588\phi \approx -0.588 radians.
  4. Rewrite the expression:

    • Substitute AA and ϕ\phi into Asin(ωt+ϕ)A\sin(\omega t + \phi): 13sin(ωt33.69)\sqrt{13}\sin\left(\omega t - 33.69^\circ\right)

Phasor Representation:

In phasor form, this can also be expressed as a complex number:

P=Aejϕ=13ej33.69\mathbf{P} = A e^{j\phi} = \sqrt{13} e^{-j33.69^\circ}

or equivalently:

P=13(cos(33.69)+jsin(33.69))\mathbf{P} = \sqrt{13} \left(\cos(-33.69^\circ) + j\sin(-33.69^\circ)\right)

Final Result:

3sin(ωt)2cos(ωt)=13sin(ωt33.69)\boxed{3\sin(\omega t) - 2\cos(\omega t) = \sqrt{13}\sin\left(\omega t - 33.69^\circ\right)}

Would you like a detailed derivation or clarification on any part? 😊


Relative Questions:

  1. What is the significance of phasor form in signal analysis?
  2. How can we convert phasor form back into its time-domain representation?
  3. What are other methods to find the magnitude and angle of a sinusoidal expression?
  4. How does the sign of the angle affect the phase shift direction?
  5. Can this conversion process be extended to include damped sinusoids?

Tip:

When converting sinusoidal functions to phasor form, always ensure the coefficients are properly handled for signs and quadrants when calculating the angle ϕ\phi.

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Math Problem Analysis

Mathematical Concepts

Trigonometry
Phasor Representation
Complex Numbers

Formulas

Phasor form: A*sin(ωt + φ) = A*sin(ωt)*cos(φ) + A*cos(ωt)*sin(φ)
Magnitude: A = sqrt(a^2 + b^2)
Phase angle: φ = arctan(b/a)

Theorems

Pythagorean Theorem (used in magnitude calculation)
Trigonometric Angle Addition Identity

Suitable Grade Level

Grades 11-12 or early college