For which of the following curves, the line x+3y=23 is the tangent at the point (233,21)?
Solutions · 1
Official solution
Check D: (233)2+9(21)2=427+49=9 , point lies on the curve.
Tangent to x2+9y2=9 at (x0,y0): xx0+9yy0=9. At the given point: 233x+29y=9⇒x+3y=23 --- matches exactly.