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Need help with this trigonometric question involving r cos(2x + a). Confused Watch

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    (Original post by bryan966)
    Hey there. This is what my mom's colleague got. I'm a bit confused whether is a valid solution. A lil warning tho, it takes time to know which part comes first. Cheers
    OK, squaring and rearranging so everything contains either cos^2 x or sinxcosx will let you use a cos(2x + a) type expansion on it and solve. I can't believe this would be taught as a practical technique though - you're making the problem more difficult just to go back and solve it in a different way!

    Also, when you square an equation you have to make sure you don't generate any spurious solutions e.g. if you start with A = 4 then A^2 = 16, but the second equation would also be solved by A = -4.

    there s wrong working at blue line. the expansion din complete

    The question in that form just seems kind of pointless. The point of this technique is to allow you to isolate x by writing the original equation in terms of one trig function which then can be inverted.

    This Q is like saying here is a question with a standard solution technique but we want you to do something obscure and pointless.

    Hence, it is almost certainly a misprint or typo of some kind.
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