bobot

I need to calculate the wavelenght of a ball travelling that is 0.435 kg and travells at 36 m/s. To calculate this i used the equations of the first picture where i put the two first functions equal to each other as they are both equal to E. If i then substitute c in the second function i become h.v = m. wavelenght^2.v^2. And after some rearranging we become wavelenght = the sqaure root of (h/(v.m)). but if i looked further into my formulas there was this exact same formula but without the square root. Is there a reason that i cant equal the two first fuctions because i dont understand why it does not work.