Solving Quadratics using a Calculator (Cambridge (CIE) IGCSE International Maths: Extended): Revision Note

Solving Quadratics using a Calculator

How do I solve quadratic equations using my calculator?

• Your graphic display calculator is able to solve quadratic equations

• Within the menu you will find an option for solving a polynomial

  • This may be within the equation solver section on some models

• Select the degree or order of polynomial you are solving

  • When solving a quadratic, the degree or order is 2

• Type in the coefficients of the quadratic you are solving

  • This is usually in the format

    • $a_2{x}^2+a_{1}x+a_0=0$ or

    • $a{x}^2+bx+c=0$

  • E.g. To solve $x^2+6x-4=0$

    • $a_2=1,a_1=6,a_3=-4$ or

    • $a=1,b=6,c=-4$

  • You must therefore rearrange the equation you are solving to this format ( ... = 0)

• Then press enter or solve to view the solutions

Should I round my answers?

• Your graphic display calculator will present answers in exact form where possible

  • E.g. $-3+\sqrt{13}$ rather than 0.6055512755...

    • Your calculator will be able to switch between the exact form and a decimal

  • If there is further working to be done using this answer

    • it is best to keep it in an exact form

  • If the solutions to the quadratic are the final answers for the question

    • check the question to see if it requests an exact answer

    • or a decimal approximation (e.g. to three significant figures)

Should I show my working when using a calculator to solve a quadratic?

• In a calculator paper it is expected that you use your calculator to solve quadratic equations

• Therefore you do not need to show working (such as using the quadratic formula)

• However, you should write down:

  • The equation you are entering into your calculator (and any prior rearranging)

  • Both solutions found by your calculator

    • In exact form where possible

• This will ensure you receive as many method marks as possible, in case of an error