Simultaneous equations 1

Simultaneous equations

• Simultaneous equations have two unknowns
• You need to find the values for the two unknowns which make both equations true

Algebraic solution

• Number each equation
• If necessary, multiply the equations so that the coefficients of one unknown are the same
• Add or subtract the equations to eliminate that unknown
• Once one unknown is found use substitution to find the other
• Check the answer by substituting both values into the other equation

Easier eliminations

• You can save time by choosing the right unknown to eliminate
• Look for one of these
  • If an unknown appears on its own in one equation you only need to multiply one equation to eliminate that unknown
  • If an unknown has different signs in the two equations tou can eliminate by adding

Check it

• Always use the equation you didn’t substitute into to check your answer

Graphical solution

• You can solve these simultaneous equations by drawing a graph
• The coordinates of the point of intersection give the solution to the simultaneous equation

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