Basic Engineering Mathematics, Fifth Edition

164 Basic Engineering Mathematics

11. The currentiflowing in a discharging capacitor
    varies with timetas shown.

i(mA) 50.0 17.0 5.8 1.7 0.58 0.24

t(ms) 200 255 310 375 425 475

Show that these results are connected by the

law of the formi=Ie

t

T whereIis the initial

current flowing andTis a constant. Determine

approximate values of constantsIandT. (15)

12. Solve, correct to 1 decimal place, the quadratic
    equation 2x^2 − 6 x− 9 =0 by plottingvalues ofx
    fromx=−2tox=5. (8)


13. Plot the graph of y=x^3 + 4 x^2 +x−6for
    values of x between x=−4andx=2.
    Hence determine the roots of the equation
    x^3 + 4 x^2 +x− 6 = 0. (9)


14. Plot a graph ofy= 2 x^2 fromx=−3tox=+ 3
    and hence solve the following equations.
    (a) 2x^2 − 8 = 0
    (b) 2x^2 − 4 x− 6 = 0 (10)