Systems of equations with substitution: -3x - 4y = -2 and y = 2x - 5 (Full video)

Khan Academy

Supporting grades: 8

Description: Sal demonstrates how to solve the system of equations -3x - 4y = -2 and y = 2x - 5 using the substitution method. So that it's less likely that we get shown up by talking birds in the future, we've set a little bit of exercise for solving systems of equations with substitution. So, what's neat about this is that they've already solved the second equation. We can take this constraint, the constraint on y in terms of x and substitute it for y in this first blue equation and then solve for x.

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