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    Isn't it if second derivative is +ve then it's minima and if it's -ve then it's maxima? Here's my working, mark scheme says maxima but I got a positive value for f''(x). Please help

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    (Original post by Taffss)
    Isn't it if second derivative is +ve then it's minima and if it's -ve then it's maxima? Here's my working, mark scheme says maxima but I got a positive value for f''(x). Please help

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    Your initial statement is correct. There is an error in your working when you differentiated -12cos2(x)sin(x)
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    (Original post by joostan)
    Your initial statement is correct. There is an error in your working when you differentiated -12cos2(x)sin(x)
    I rechecked it again and I think it's the sign problem, Instead I should've kept +ve cosx let me check
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    (Original post by joostan)
    Your initial statement is correct. There is an error in your working when you differentiated -12cos2(x)sin(x)
    I made cosx +ve and got -ve for f''(x) therefore max. Thanks
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    (Original post by Taffss)
    I made cosx +ve and got -ve for f''(x) therefore max. Thanks
    Well done
    NP
 
 
 
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