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Lesson · Grade 7 · Mathematics

Checking a Solution by Substituting

  • Grade 7
  • Mathematics
  • 1 min 10 s
  • British Columbia
  • BC7-MA-44

The video asks whether x = 7 is the solution of 3x + 5 = 26, splits the equation into a left-side and right-side table, and substitutes 7 for x: 3 × 7 + 5 = 21 + 5 = 26, which matches the right side, so x = 7 is correct. A quick check of x = 6 gives 23, which is not 26, and the video ends on the one-line recap "Substitute, then compare both sides".

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In one sentence

The question this lesson answers

Is x equals 7 the solution of 3x plus 5 equals 26?

Every equation has a left side and a right side.

Transcript

What the lesson says

Is x equals 7 the solution of 3x plus 5 equals 26?

Every equation has a left side and a right side.

If x equals 7 is the solution, the two sides will be equal.

To check, substitute 7 for x and work out each side.

3x means 3 times x, so the left side becomes 3 times 7 plus 5.

Multiply first: 3 times 7 is 21.

Then add: 21 plus 5 is 26.

The left side is 26, and the right side is 26 too.

Both sides are equal, so x equals 7 is the solution.

If we try x equals 6 instead, the left side is 3 times 6 plus 5, which is 23.

23 is not 26, so x equals 6 is not the solution.

To check a solution, substitute it into the equation and see if both sides are equal.

Curriculum

Where this fits

British Columbia, Grade 7

Mathematics, Patterns and algebra: two-step equations with whole-number coefficients, constants, and solutionsBC7-MA-44

Previous: Two-Step Equations: Undo Each StepNext: Writing an equation from a word problem

The outcomes and strands follow the British Columbia curriculum.

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