A common tangent to `9x^2-16y^2 = 144` and `x^2 + y^2 = 9`, is

Equation of a common tangent to x^(2)+y^(2)=16" and "9x^(2)+25y^(2)=225 is :

Equation of common tangent of 9x^(2)+16y^(2)=144,y^(2)-x+4=0 and x^(2)+y^(2)-12x+32=0 is

" Equation of common tangent of "9x^(2)+16y^(2)=144,y^(2)-x+4=0" and "x^(2)+y^(2)-12x+32=0" is "

The lenth of the portion of the common tangent to x^(2)+y^(2)=16 and 9x^(2)+25y^(2)=225 between the two points of contact is

The lenth of the portion of the common tangent to x^(2)+y^(2)=16 and 9x^(2)+25y^(2)=225 between the two points of contact is

If x=k is the equqtion of a common tangent to the curves 9x^(2)+16y^(2)=144 ,y^(2)-x+4=0 and x^(2)+y^(2)-12x+32=0 then k is equal to _____