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C4 AQA r alpha method HELP!!!

Hi! i am a bit confused on the r alpha method
i understand how to work out the r and the alpha part and also the minimum and the maximum however i just cant work out the value of x for the minimum

here is a question:
cosx + 3sinx in the form rcos(x-a)
i worked out it equals sqr-root 10cos(x-1.249)
the minimum point is - sqrroot10
but how would i go about finding the value x is at the minimum

thanks! :smile:
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mikelbird
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Original post by the_sky.
Hi! i am a bit confused on the r alpha method
i understand how to work out the r and the alpha part and also the minimum and the maximum however i just cant work out the value of x for the minimum

here is a question:
cosx + 3sinx in the form rcos(x-a)
i worked out it equals sqr-root 10cos(x-1.249)
the minimum point is - sqrroot10
but how would i go about finding the value x is at the minimum

thanks! :smile:


Well you have a cosine graph shifted 1.249 radians to the right (and with an amplitude of sqrt 10). Where normally would the first minimum occur if it had not been shifted?? Think about your graph of a cosine curve. Now that point is shifted 1.249 radians to the right.....so....

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