HP 39g hp 39g+ (39g & 40g)_mastering the hp 39g+_English_E_F2224-90010.pdf - Page 148
Using Stats to find equations from point data, Quadratic, Auto Scale, Exponential
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Using Stats to find equations from point data eg. 1 Find the equation of the quadratic which passes through the points (1,5), (3,15) and (-5,71). In the Statistics aplet, choose mode and enter the data. Now change to the SYMB SETUP view and choose the Quadratic data model. Change to the PLOT view using the VIEWS Auto Scale option and press the key. Don't worry that the scale is not good because we don't care about the graph. It only needs to be drawn in order to calculate the fit equation. Finally, change back to the SYMB view and see the equation, pressing if necessary. eg. 2 A population of bacteria is known to follow a growth pattern governed by the equation N = N0ekt ;t ≥ 0 . It is observed that at t = 3 hours, there are 100 colonies of bacteria and also that at t = 10 hours there are 10 000 colonies. (i) Find the values of N0 and of k. (ii) Predict the number of bacteria colonies after 15 hours. (iii) How long does it take for the number of colonies to double? (i) Find N0 and k. Start up the Statistics aplet, set it to and enter the data given. Change to the SYMB SETUP view and specify an Exponential model for the data. 148