help........

i have Three questions which i really don't know how to do

pls help me!!

solve the given quadratic equations by completing the square.

$\displaystyle

(1)----v(v + 2) = 15

$

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$\displaystyle

(2)----5T^2 - 10T + 4 = 0

$

$\displaystyle (3)$In machine design. in finding the outside diameter$\displaystyle D_o$ of a hollow shaft, the equation$\displaystyle D_o^2 - DD_o - 0.25D^2 = 0$ is used Solve for $\displaystyle D_o$ if $\displaystyle D = 3.625cm$