Substitution Method

Idea of substitution

Make one variable the subject in one equation, then substitute that expression into the other equation.

Example:
y = 2x + 1 -- (1)
3x + 2y = 12 -- (2)
Sub (1) into (2): 3x + 2(2x + 1) = 12
3x + 4x + 2 = 12   ⇒   7x = 10   ⇒   x = 10/7
Sub into (1): y = 2(10/7) + 1 = 20/7 + 7/7 = 27/7

Best when: One equation already has x or y with coefficient 1 or -1.

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