I’m stuck on this one please help

Which values for a and b will create infinitely many solutions for this system of equations? ax-y=8 2x+y=b

Find the gradient of f(x,y,z)equals=left parenthesis x squared plus y squared plus z squared right parenthesis superscript negative 1 divided by 2 baseline plus ln left parenthesis x right parenthesis x2+y2+z2−1/2+ln(xyz) at the point left parenthesis negative 2 comma 1 comma negative 2 right parenthesis(−2,1,−2).

Write an equation in point-slope form for the line through the given point that has the given slope (-2,-7); m=-3/2