The following system of equations $$$x+y+z=3,$$$ $$$x+2y+3z=4,$$$ $$$x+4y+kz=6$$$
will not have a unique solution for $$k$$ equal to

A wastewater sample contains $$10^{-5.6}$$ mol/l of OH^- ions at $$25^o$$ C. The pH of this sample is

The type of surveying in which the curvature of the earth is taken into account is called

The base width of an elementary profile of gravity dam of height H is b. The specific gravity of the material of the dam is G and uplift pressure coefficient is K. the correct relationship for no tension at the heel is given by