Stepwise
Start practisingPractise

WAEC 2023 · Paper 2 · Q4

An equation of a circle is 3x2+3y2+6x+2my−18=03x^2 + 3y^2 + 6x + 2my - 18 = 0, where mm is a constant. If the radius of the circle is 10\sqrt{10} units, find the positive value of mm.

  1. (a)

    Positive value of mm

Worked solution (try it first)
  1. Divide by 3: x2+y2+2x+2m3y−6=0x^2 + y^2 + 2x + \frac{2m}{3}y - 6 = 0, so g=1g = 1 and f=m3f = \frac{m}{3}.
  2. r2=g2+f2−cr^2 = g^2 + f^2 - c: 10=1+m29+610 = 1 + \dfrac{m^2}{9} + 6.
  3. m29=3\dfrac{m^2}{9} = 3, so m2=27m^2 = 27 and m=33≈5.196m = 3\sqrt3 \approx 5.196 (the positive value).

Report a problem with this question