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# core 3 question help!!!!! watch

1. the equation of a curve is y=2xsq - lnx, where x>0. find by differentiation the x-coordinate of the stationary point on the curve, and determine whether this point is a maximum or a minimum point.

so basically i've done the first part and got

dy/dx = 4x - 1/x = 0 when x = 1/2 which is correct

but when I d2y/dx2 the equation i get 4 - 1/xsq

not when i put x = 1/2 into that equation it comes out as 4 - 1/(1/4) which = 0
unless i've done something very wrong i have no idea how to work out whether its a maximum or minimum, the answer in the back says minimum

so if someone could help me i would be very grateful!!!!
xxx
2. You made a minus sign error.
3. (Original post by setsunarules)
the equation of a curve is y=2xsq - lnx, where x>0. find by differentiation the x-coordinate of the stationary point on the curve, and determine whether this point is a maximum or a minimum point.

so basically i've done the first part and got

dy/dx = 4x - 1/x = 0 when x = 1/2 which is correct

but when I d2y/dx2 the equation i get 4 - 1/xsq

not when i put x = 1/2 into that equation it comes out as 4 - 1/(1/4) which = 0
unless i've done something very wrong i have no idea how to work out whether its a maximum or minimum, the answer in the back says minimum

so if someone could help me i would be very grateful!!!!
xxx
Should be 4x plus 1-x sq
4. thank you so much!!! <33

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