12.4 Solving quadratic equations by factorising — Practise

1. Solve $x^2+5x+6=0$.

Answer: $x=-2$ or $x=-3$.

2. Solve $x^2-7x+12=0$.

Answer: $x=3$ or $x=4$.

3. Solve $x^2=16$.

Answer: $x=-4$ or $x=4$.

4. Solve $x^2+x-12=0$.

Answer: $x=-4$ or $x=3$.

5. Solve $x^2+2x=15$.

Answer: $x=-5$ or $x=3$.

6. A rectangle has area $18\text{ cm}^2$ and sides $x$ cm and $(x+3)$ cm. Find positive $x$.

Answer: $x=3$ cm because a length is positive.

7. Solve $2x^2-8x=0$.

Answer: $x=0$ or $x=4$.

8. Solve $(x-1)(x+6)=0$.

Answer: $x=1$ or $x=-6$.