+893 Hi Melody
As Alan has said $$r\angle \theta$$ is a shorthand notation used mainly by electrical engineers.
It's actually shorthand for the complex number $$r(\cos \theta + \imath \sin \theta).$$
Written out in full, we would have
$$r_{1}\angle \theta_{1}\times r_{2}\angle\theta_{2}\\=r_{1}r_{2}(\cos\theta_{1}+\imath\sin\theta_{1})(\cos\theta_{2}+\imath\sin\theta_{2})\\=r_{1}r_{2}(\cos\theta_{1}\cos\theta_{2}-\sin\theta_{1}\sin\theta_{2}+\imath(\sin\theta_{1}\cos\theta_{2}+\cos\theta_{1}\sin\theta_{2}))\\=r_{1}r_{2}(\cos(\theta_{1}+\theta_{2})+\imath\sin(\theta_{1}+\theta_{2}))\\=r_{1}r_{2}\angle(\theta_{1}+\theta_{2}).$$
+33615 Multiply the magnitudes together and add the angles:
100∠30*(-10∠-165) = -(100*10)∠(30-165) = -1000∠-135
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+33615 Electrical engineers commonly use this sort of representation for the magnitude and phase of ac electrical currents; but in general you could use it for any two-dimensional vectors expressed in polar coordinates.
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+118608 Mmm, thanks Alan, I still don't have any concept of what it means.
Does it have a pictorial representation or a situation word problem that I could understand where it would be useful?
+33615 If a vector is given in polar coordinates by (r, θ) then it can also be written as r∠θ (which electrical engineers do a lot!).
Multiplying two together is just a combined stretching (r1*r2) and rotating (θ1 + θ2) transformation.
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+893 Hi Melody
As Alan has said $$r\angle \theta$$ is a shorthand notation used mainly by electrical engineers.
It's actually shorthand for the complex number $$r(\cos \theta + \imath \sin \theta).$$
Written out in full, we would have
$$r_{1}\angle \theta_{1}\times r_{2}\angle\theta_{2}\\=r_{1}r_{2}(\cos\theta_{1}+\imath\sin\theta_{1})(\cos\theta_{2}+\imath\sin\theta_{2})\\=r_{1}r_{2}(\cos\theta_{1}\cos\theta_{2}-\sin\theta_{1}\sin\theta_{2}+\imath(\sin\theta_{1}\cos\theta_{2}+\cos\theta_{1}\sin\theta_{2}))\\=r_{1}r_{2}(\cos(\theta_{1}+\theta_{2})+\imath\sin(\theta_{1}+\theta_{2}))\\=r_{1}r_{2}\angle(\theta_{1}+\theta_{2}).$$
