WAEC Further Mathematics 2020 Paper

Concept:For an equation to represent a circle, the coefficients of $x^2$ and $y^2$ must be equal, and there must be no $xy$ term.Explanation:Check each equation for these conditions.Option A: $3x^2 + 3y^2 + 5x + 7y = 5$. Divide by $3$; coefficients of $x^2$ and $y^2$ are equal, so it is a circle.Option B: $x^2 + y^2 + 5x + 4y = 0$. Coefficients are both $1$, so it is a circle.Option C: $5x^2 + 5y^2 - 16 = 0$. Divide by $5$; coefficients are equal, so it is a circle.Option D: $x^2 - y^2 + 3x - 5y = 2$. The coefficients are $+1$ and $-1$. Since they are not equal, it cannot be a circle; it represents a hyperbola.Answer:D. $x^2 - y^2 + 3x - 5y = 2$