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# prove that: cos x − cos (x − π/3 ) ≡ cos (x + π/ 3 ) watch

1. ??
2. You will probably find answers faster in the Maths Help Forum
3. I think you are supposed to use the identities for cos(a +/- b) and simplify it.

I tried it and its not coming for me. lel..
4. (Original post by missdentist10)
??
Don't know what constitutes "proof" at the level of maths you are studying
1. Carefully using the addition formula for cos(A + B) on both sides of your equation you can show LHS=RHS
Or
2. Use the addition formula on the LHS, then use your preferred method to rewrite the result in the form Rcos(x+theta)
Remember pi/3 is a special angle with exact trig values.

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